Printing system, print controller, printing apparatus, method of controlling printing operation, method of printing, ink cartridge, ink supplier, and recording medium

ABSTRACT

A technique of the present invention uses dark yellow (DY) ink, in addition to a plurality of conventionally used basic color inks including cyan (C) ink, magenta (M) ink, and yellow (Y) ink. The technique may cause a printer to create dots with the DY ink, in place of creation of dots with the Y, C, and M inks. This arrangement enhances the degree of freedom in specification of dot on-off conditions of the respective inks, and relieves the restriction of ink duty, thereby enabling a resulting printed image to have higher picture quality.

This is a continuation of application Ser. No. 09/539,886 filed Mar. 31,2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a technique of forming an adequatedistribution of ink dots of respective colors on a printing medium, soas to print an image expressed in a wide range of natural colors.

2. Description of the Related Art

In a printing apparatus that ejects ink droplets of various color inksfrom a print head and thereby expresses an image of natural colors on aprinting medium, four color inks, that is, cyan (C), magenta (M), yellow(Y), and black (K), are basically used to create ink dots and print animage. The printing apparatus regulates the hue and the lightness, whichare indexes representing the color, so as to print an image expressed ina wide range of natural colors. The hue, that is, the ‘color’ or ‘tint’,such as red or blue, is regulated by changing the ratio of dots of theC, M, and Y inks ejected from the print head. The lightness is, on theother hand, regulated by changing the density of dots. Regulating theratio and the density of dots created with the respective color inks onthe printing medium enables a printed image to have a wide range ofnatural colors.

Some recently developed printing apparatus use light cyan (LC) ink andlight magenta (LM) ink, (additionally light yellow (LY) ink in somecases) in addition to the above four basic color inks, so as tosignificantly improve the picture quality in an area of high lightness.In the case where an image in the area of high lightness (that is, thehighlighted area) is printed with only four color inks, C, M, Y, and K,a sparse distribution the C and M dots undesirably makes these dotsconspicuous and thereby lowers the picture quality of the printed image.The phenomenon of making the dots conspicuous to worsen the picturequality is expressed by the term ‘poor granularity’. It is difficult toreproduce the image information with regard to a fine part with thesparsely distributed dots. This is also the reason of the poor picturequality of the resulting printed image with only the four color inks, C,M, Y, and K. The dots of the LC and LM inks (additionally LY ink in someoccasions) are, on the other hand, not so conspicuous as the dots of theC and M dots and thereby do not lower the picture quality of thehighlighted area. The LC and LM inks enable the dots to be formed at ahigher density than the C and M inks. This accordingly enablesreproduction of the image information with regard to the fine part andfurther improves the picture quality. Because of these reasons, theprinting apparatus using the six color inks including the LC and LY inks(or the seven color inks further including the LY ink) improves thepicture quality of the highlighted area.

The prior art printing apparatus including those using the light inks,however, can not sufficiently improve the picture quality in an area oflow lightness (that is, the shadow area), because of the reasonsdiscussed below. Especially the printing apparatus using the light inkshave an insufficient improvement in picture quality in the shadow area,while significantly improving the picture quality in the highlightedarea.

This problem is explained with an example of a gradation pattern fromred to black with a gradual decrease in lightness. The color ‘red’ isreproduced by mixture of magenta dots and yellow dots. The lightness islowered by addition of cyan dots or black dots. Formation of black dotson red dots makes the black dots extremely conspicuous in an areasupposed to have a homogeneous color. This results in the poorgranularity. The dots of cyan, which is complementary to red, are alsorather conspicuous on the red dots, although the degree ofconspicuousness is lower than that of the black dots. Formation of cyandots on red dots thus also results in the rather poor granularity. As inthe case of the highlighted area, the use of the light cyan inkeffectively improves the granularity. From the viewpoint of theimprovement in granularity, the light cyan ink is most preferable overthe cyan ink and the black ink to form dots over the red dots. Additionof the cyan dots or the black dots on the red dots having a sufficientlylow lightness, however, does not make the cyan dots or the black dots soconspicuous but keeps the granularity at a fair level.

There is a restriction of total quantity of ink ejected per unit area onthe printing medium, and it is impossible to heighten the density of dotformation limitlessly. This restriction is referred to as therestriction of ink duty. Ejection of ink over the allowed density ofdots causes blots or wrinkles on the printing medium. In order to avoidsuch problems, each printing medium has a preset maximum density of dots(restriction of ink duty). The total density of dots created with therespective inks should not exceed this restriction of ink duty.

When the gradation pattern from red to black is printed, it is requiredto add the light cyan dots or the cyan dots. The color ‘red’ isoriginally expressed by a large number of yellow dots and magenta dotsas mentioned previously. Formation of even a small number of light cyandots or cyan dots thus causes the total quantity of ink to reach therestriction of ink duty. In the course of the gradation, there isaccordingly a prohibition of further addition of the light cyan dots orthe cyan dots. In the practical operation, when there is some margin forthe restriction of ink duty, light cyan dots are added to red dots tolower the lightness. When the total quantity of ink reaches therestriction of ink duty, even if the cyan dots may have adverse effectson the granularity of the resulting printed image, the cyan dots insteadof the light cyan dots should be formed to further decrease thelightness. When the total quantity of ink again reaches the restrictionof ink duty under the condition of the perfect replacement of the lightcyan dots with the cyan dots, even if the black dots are conspicuous,the black dots instead of the cyan dots should be formed to furtherdecrease the lightness. In the shadow area (the area of low lightness)having the gradation from red to black, the cyan dots and the black dotsare often used irrespective of their conspicuousness, because of therestriction of ink duty. This naturally results in the poor granularity.

The above description regards the example of printing the gradationpattern from red to black. The formation pattern of ink dots should bespecified under the various limitations including the improvement ingranularity and the restriction of ink duty. The design of the optimumdot formation pattern accordingly requires a lot of time and labor withthe trial and error.

SUMMARY OF THE INVENTION

The object of the present invention is thus to enhance the degree offreedom in specification of dot on-off conditions with regard to aplurality of different inks and thereby improve the picture quality in aspecific area including a low lightness area (shadow area).

At least part of the above and the other related objects is actualizedby a printing system, which includes a printer that creates dots with aplurality of different inks, so as to print an image on a printingmedium, and a print controller that supplies control information to theprinter, so as to control the creation of dots with the plurality ofdifferent inks. The print controller includes: a dot on-off conditionspecification unit that specifies dot on-off conditions with regard to aplurality of basic color inks and a dark ink based on input image data,the plurality of basic color inks being combined with one another toexpress achromatic color, the dark ink having a main wavelength regionof light absorption substantially identical with that of one basic colorink selected out of the plurality of basic color inks but a lowerlightness than that of the selected basic color ink; and a controlinformation output unit that outputs the specification of the dot on-offconditions with regard to the plurality of basic color inks and the darkink to the printer as the control information. The printer includes: acontrol information input unit that receives the specification of thedot on-off conditions with regard to the plurality of basic color inksand the dark ink, which is output from the control information outputunit, as the control information; and a dot formation unit that createsdots with the plurality of basic color inks and the dark ink, based onthe input control information.

The present invention is also directed to a method of printing, whichcorresponds to the printing system discussed above. The presentinvention accordingly provides a method of creating dots with aplurality of different inks, so as to print an image on a printingmedium. The method includes the steps of: specifying dot on-offconditions with regard to a plurality of basic color inks and a dark inkbased on input image data, the plurality of basic color inks beingcombined with one another to express achromatic color, the dark inkhaving a main wavelength region of light absorption substantiallyidentical with that of one basic color ink selected out of the pluralityof basic color inks but a lower lightness than that of the selectedbasic color ink; and creating dots with the plurality of basic colorinks and the dark ink, based on the specification of the dot on-offconditions with regard to the plurality of basic color inks and the darkink, so as to print an image.

In the printing system and the corresponding method of the presentinvention, the dot on-off conditions with regard to the plurality ofbasic color inks and the dark ink are specified, based on the inputimage data. Here the plurality of basic color inks are combined with oneanother to create ink dots and thereby express achromatic color. Thedark ink includes one basic color ink selected out of the plurality ofbasic color inks as a primary component and another ink having aspecific hue different from the hue of the selected basic color ink. Thedark ink has a lower lightness than that of the selected basic colorink. The dark ink may alternatively have a different ink compositionfrom that of the selected basic color ink but equivalent spectroscopiccharacteristics to those of the selected basic color ink. When theselected basic color ink is yellow ink, for example, the dark ink may beobtained by adding adequate quantities of cyan and magenta dyes to theyellow ink or by adding an adequate quantity of black dye to the yellowink. The technique of the present invention creates dots with theplurality of basic color inks and the dark ink on the printing medium,based on the specification of dot on-off conditions with regard to therespective inks, so as to print an image. This arrangement enables dotsto be created with the dark ink having the characteristics discussedabove, as well as with the plurality of basic color inks. This enhancesthe degree of freedom in specification of dot on-off conditions andthereby improves the picture quality of a resulting printed image.Specifying the dot on-off conditions with regard to not only the basiccolor inks but the dark ink results in improving the picture quality,because of the functions discussed below.

As mentioned above, the dark ink includes one basic color ink selectedout of the plurality of basic color inks as a primary component andanother ink having a specific hue different from the hue of the selectedbasic color ink, and has a lower lightness than that of the selectedbasic color ink. A certain color conventionally expressed by acombination of the plurality of basic color inks may be expressible byonly the dark ink or by a combination of the dark ink with smallquantities of one or plural basic color inks. In such cases, expressionof the certain color by the combination of the dark ink with one orplural basic color inks requires a less total quantity of inks, comparedwith the expression of the certain color by the combination of theplurality of basic color inks. The use of the dark ink thus improves thepicture quality, which is worsened by the restriction of ink duty. Forexample, the use of the dark ink desirably keeps the fair granularity ina shadow area, where the granularity is readily worsened by therestriction of ink duty.

A print controller of the present invention is applicable to such aprinting system. The present invention is accordingly directed to aprint controller that supplies control information to a printer, whichcreates dots with a plurality of different inks, in order to control thecreation of dots with the plurality of different inks. The printercreates dots with a plurality of basic color inks as well as with a darkink, wherein the plurality of basic color inks are combined with oneanother to express achromatic color, and the dark ink has a mainwavelength region of light absorption substantially identical with thatof one basic color ink selected out of the plurality of basic color inksbut a lower lightness than that of the selected basic color ink. Theprint controller includes: a dot on-off condition specification unitthat specifies dot on-off conditions with regard to the plurality ofbasic color inks and the dark ink, based on input image data; and acontrol information output unit that outputs the specification of thedot on-off conditions with regard to the plurality of basic color inksand the dark ink to the printer as the control information.

The present invention is further directed to a method of controlling aprinting operation, which corresponds to the print controller discussedabove. The present invention accordingly provides a method of supplyingcontrol information to a printer, which creates dots with a plurality ofdifferent inks on a printing medium, in order to control the creation ofdots with the plurality of different inks and thereby controlling aprinting operation of the printer. The method includes the steps of: (a)specifying dot on-off conditions with regard to a plurality of basiccolor inks and a dark ink based on input image data, the plurality ofbasic color inks being combined with one another to express achromaticcolor, the dark ink having a main wavelength region of light absorptionsubstantially identical with that of one basic color ink selected out ofthe plurality of basic color inks but a lower lightness than that of theselected basic color ink; and (b) outputting the specification of thedot on-off conditions with regard to the plurality of basic color inksand the dark ink to the printer as the control information, so as tocontrol the printing operation of the printer.

In the print controller and the corresponding method of controlling theprinting operation, the dot on-off conditions with regard to theplurality of basic color inks and the dark ink are specified, based onthe input image data. The specification of the dot on-off conditions issupplied to the printer as the control information to control creationof dots with the plurality of basic color inks and the dark ink.

The technique of the present invention provides the plurality of basiccolor inks and the dark ink in the printer, which creates dots with aplurality of different inks on a printing medium, and supplies thecontrol information to the printer. This arrangement enables creation ofink dots with the plurality of different inks including the dark ink,thus printing an image of high picture quality.

In accordance with one preferable application of the print controllerand the corresponding method of controlling the printing operation, acolor conversion table is provided to store mappings of tints used toexpress a color image to combinations of the plurality of basic colorinks and the dark ink to represent the tints. In this application, thedot on-off conditions with regard to the plurality of basic color inksand the dark ink are specified by referring to the color conversiontable.

The method of referring to the color conversion table enables the doton-off conditions of the respective inks to be specified quickly andaccurately.

In accordance with another preferable application of the printcontroller, the dot on-off conditions with regard to the plurality ofbasic color inks and the dark ink are specified, based on a presetproportion regarding dots of the plurality of basic color inks and dotsof the dark ink.

When the dot on-off conditions are specified with regard to the dark inkas well as the plurality of basic color inks, the proportion of the dotswith the respective inks may take a variety of values. The arrangementof specifying the dot on-off conditions based on the proportion setequal to an appropriate value enables an image of high picture qualityto be printed.

In accordance with still another preferable application of the printcontroller, the dark ink has lower lightness and saturation than thoseof one basic color ink selected out of the plurality of basic colorinks. The dark ink is obtained, for example, by adding the dye ofanother ink to the selected basic color ink.

The use of the dark ink enhances the degree of freedom in specificationof the dot on-off conditions and thereby improves the picture quality ofthe resulting printed image. The use of the dark ink, which is obtainedby adding at least one dye of another ink to lower the lightness and thesaturation, may enable a specific color conventionally expressed by acombination of the plurality of basic color inks to be expressed by onlythe dark ink or by a combination of the dark ink with small quantitiesof one or plural basic color inks. The expression of the specific colorby the combination of the dark ink with the basic color inks reduces thetotal quantity of inks and thus improves the picture quality, which isworsened by the restriction of ink duty.

The dark ink may alternatively have a main wavelength region for moststrongly absorbing a ray in a visible range, which is substantiallyidentical with that of one basic color ink selected out of the pluralityof basic color inks, and a greater integral of light absorptivity in awavelength region of the visible range than that of the selected basiccolor ink.

The use of the dark ink enhances the degree of freedom in specificationof the dot on-off conditions and thereby improves the picture quality ofthe resulting printed image.

The main wavelength region for most strongly absorbing a ray in avisible range is approximately equal to a range of 600 nm to 700 nm toabsorb a red ray in the case of cyan ink, equal to a range of 500 nm to600 nm to absorb a green ray in the case of magenta ink, and equal to arange of 400 nm to 500 nm to absorb a blue ray in the case of yellowink. Since the absorptivity of light gently varies, the half-width (thatis, the wavelength region having the absorptivity that is half themaximum absorptivity) may be adopted in the case where there is adifficulty in identifying the wavelength region.

The dark ink may have the main wavelength region, which is mostlyincluded in a wavelength region of 400 nm to 500 nm, and a smaller lightabsorptivity in the vicinity of 700 nm than a mean light absorptivity ina wavelength region of 600 nm to 700 nm.

It is known that the sensitivity of the vision of human eye to the colorgradually lowers in a wavelength range of about 650 nm and issignificantly low in the vicinity of 700 nm. Irrespective of a largevariation in spectroscopic characteristics of the ink in the vicinity ofthe wavelength of 700 nm, there is no significantly difference in huerecognized by the vision of the human eye. Namely the spectroscopiccharacteristics of the ink have a large degree of freedom in thevicinity of the wavelength of 700 nm. The ink having a favorable hue isthus prepared by utilizing this large degree of freedom. The dark inkhaving the favorable hue has the smaller light absorptivity in thevicinity of 700 nm than the mean light absorptivity in the wavelengthregion of 600 nm to 700 nm. The main wavelength region that is mostlyincluded in the wavelength region of 400 nm to 500 nm is substantiallyopposite to the range in the vicinity of 700 nm having the large degreeof freedom across the visible range. This facilitate the design of theink.

The dark ink may have the main wavelength region, which is mostlyincluded in a wavelength region of 400 nm to 500 nm, and a greater lightabsorptivity in the vicinity of 700 nm than a mean light absorptivity ina wavelength region of 600 nm to 700 nm. The greater light absorptivityin the vicinity of 700 nm than the mean light absorptivity in thewavelength region of 600 nm to 700 nm enables the dark ink to have amore preferable hue, because of the reason discussed above.

The dark ink, whose dot on-off conditions are specified by the printcontroller of the present invention may have:

(A) a characteristic wavelength region for strongly absorbing a ray in avisible range to mainly determine the hue of the dark ink, which issubstantially identical with a characteristic wavelength region of onebasic color ink selected out of the plurality of basic color inks;

(B) a mean value of light absorptivity that is greater than orsubstantially identical with a mean value of light absorptivity of theselected basic color ink in the characteristic wavelength region of thedark ink; and

(C) a mean value of light absorptivity that is greater than a mean valueof light absorptivity of the selected basic color ink in a wavelengthregion of visible light except the characteristic wavelength region ofthe dark ink.

The dark ink satisfying the above condition (A) has a hue close to thehue of the corresponding basic color ink, so that a specific colorconventionally expressed by a combination of the plurality of basiccolor inks is, in many cases, expressible by a combination of the darkink with one or plural basic color inks. Expression of the specificcolor by the combination of the dark ink satisfying the above conditions(B) and (C) with one or plural basic color inks requires the less totalquantity of inks than expression of the specific color by thecombination of the plurality of basic color inks. The use of the darkink satisfying all the above conditions (A) through (C) thus reduces thetotal quantity of ink consumption in many cases. This arrangementeffectively prevents the poor granularity and improves the picturequality, which is worsened by the restriction of ink duty as discussedpreviously.

The dark ink may have the characteristic wavelength region, which ismostly included in a wavelength region of 400 nm to 500 nm, and asmaller light absorptivity in the vicinity of 700 nm than a mean lightabsorptivity in a wavelength region of 600 nm to 700 nm.

As described above, even when the light absorptivity in the vicinity of700 nm varies, the hue of the ink recognizable by the vision of thehuman eye does not have any significant variation. It is accordinglyexpected that the spectroscopic characteristics of the ink have a largedegree of freedom in the vicinity of the wavelength of 700 nm. Thesmaller light absorptivity in the vicinity of 700 nm than the mean lightabsorptivity in the wavelength region of 600 nm to 700 nm enables thedark ink to have a more favorable hue. Setting the characteristicwavelength region of the dark ink to be substantially opposite to therange in the vicinity of 700 nm having the large degree of freedomacross the visible range facilitates the design of the ink.

The dark ink may have the characteristic wavelength region, which ismostly included in a wavelength region of 400 nm to 500 nm, and agreater light absorptivity in the vicinity of 700 nm than a mean lightabsorptivity in a wavelength region of 600 nm to 700 nm.

As described previously, there is a large degree of freedom in settingthe light absorptivity in the vicinity of the wavelength of 700 nm. Thegreater light absorptivity in the vicinity of 700 nm than the mean lightabsorptivity in the wavelength region of 600 nm to 700 nm may enable thedark ink to have a more favorable hue.

The dark ink, whose dot on-off conditions are specified by the printcontroller of the present invention, may have a hue in a specific huerange interposed between a red hue zone and a green hue zone on aMunsell hue circle, and have a lower lightness than that of a basiccolor ink out of the plurality of basic color inks, which has a hue inthe specific hue range.

The specific hue range interposed between the red hue zone and the greenhue zone on the Munsell hue circle roughly corresponds to the hue ofyellow. The color of yellow has a relatively high lightness. Dots of thedark yellow ink having the lower lightness than that of the yellow inkare still not conspicuous. Creating dots with such a dark ink thussignificantly improves the picture quality of the resulting printedimage.

The dark ink may have a hue in the specific hue range that includes ayellow hue zone and extends to a boundary between the yellow hue zoneand the green hue zone on the Munsell hue circle. The ink in thisspecific hue range has the hue of greenish yellow. Creating dots withsuch a dark ink significantly improves the picture quality of theresulting printed image having the little greenish hue.

The dark ink may have a hue in the specific hue range that includes ayellow hue zone and extends to a boundary between the yellow hue zoneand the red hue zone on the Munsell hue circle, and a smaller saturationthan that of flesh color. The ink in the specific hue range thatincludes the yellow hue zone and extends to the boundary between theyellow hue zone and the red hue zone on the Munsell hue circle has thehue of reddish yellow. Creating dots with such a dark ink significantlyimproves the picture quality of the resulting printed image having thelittle reddish hue. The color that is included in the specific hue rangeand has a relatively large saturation is close to the ‘flesh color’.When the ink having the hue of reddish yellow is used as the dark ink,it is preferable that the ink has a smaller saturation than that offlesh color. The dark ink of smaller saturation significantly improvesthe picture quality of the resulting printed image. It is accordinglypreferable that the dark ink has a hue in the specific hue range thatincludes the yellow hue zone and extends to the boundary between theyellow hue zone and the red hue zone on the Munsell hue circle, and asmaller saturation than that of flesh color.

The dark ink may have a hue included in a specific range of 10R to 10GYon a Munsell hue circle, and a lower lightness than that of a basiccolor ink out of the plurality of basic color inks, which has a hue inthe specific range.

The ink in the specific range roughly has the hue of yellow. Creatingdots with such a dark ink significantly improves the picture quality ofthe resulting printed image.

The dark ink may have a saturation of smaller than 3.5C on a Munsellchroma when the hue of the dark ink is in a range of 2.5YR to 7.5YR onthe Munsell hue circle.

The ink having the hue in the range of 2.5YR to 7.5YR on the Munsell huecircle and the saturation of greater than 3.5C on the Munsell chroma hasthe tint close to the flesh color. When an image having the greenish hueis printed, the use of the dark ink having a smaller saturation thanthat of ‘flesh color’ has better effects on improvement of the picturequality. It is accordingly preferable that the dark ink has a saturationof smaller than 3.5C on the Munsell chroma when the hue of the dark inkis in the range of 2.5YR to 7.5YR on the Munsell hue circle.

The hue of the dark ink may be in a range of 10YR to 10GY on the Munsellhue circle. The ink in this range has the hue of greenish yellow.Creating dots with such a dark ink significantly improves the picturequality of the resulting printed image having the little greenish hue.

The dark ink may have the hue in a range of 10Y to 10R on the Munsellhue circle and a saturation of smaller than 3.5C on a Munsell chroma.The ink having the hue in the range of 10Y to 10R on the Munsell huecircle and the saturation of greater than 3.5C on the Munsell chroma hasthe tint close to the flesh color. When an image having the reddish hueis printed, the use of the dark ink having a smaller saturation thanthat of ‘flesh color’ has better effects on improvement of the picturequality. It is accordingly preferable that the dark ink has the hue in arange of 10Y to 10R on the Munsell hue circle and a saturation ofsmaller than 3.5C on the Munsell chroma.

In accordance with one preferable application of the print controllerthat specifies the dot on-off conditions of the respective inks based onthe image data, the technique specifies the dot on-off conditions withregard to the plurality of basic color inks and the dark ink, as well aswith regard to at least one light ink, which has a hue substantiallyidentical with that of at least one basic color ink selected out of theplurality of basic color inks but a lower density than that of the atleast one basic color ink. The results of the specification are outputto the printer as the control information to control the creation ofdots with the plurality of different inks. The printer creates dots withthe plurality of basic color inks, the dark ink, and the at least onelight ink on a printing medium, according to the control information.

As described previously, the printing apparatus using the light inkremarkably improves the picture quality in the highlighted area but hasless effects on improvement of the picture quality in the shadow area,because of the restriction of ink duty. Additionally using the dark inkimproves the picture quality in the shadow area and thus attains theimprovement in picture quality in the whole image.

In accordance with one preferable application of the print controllerthat specifies the dot on-off conditions of the respective inks based onthe image data, the technique outputs the control information to controlthe creation of dots to a printer that creates at least twovariable-size dots having different sizes with the respective inks. Thetechnique specifies the dot on-off conditions as well as the sizes ofthe dots to be formed by the printer with regard to the plurality ofdifferent inks and supplies the results of the specification to theprinter. The printer creates the adequate size dots with the pluralityof different inks, based on the control information.

Varying the size of the ink dot by the printer that enables creation ofat least two variable-size dots having different sizes significantlyimproves the picture quality of the resulting printed image. In thisapplication, using the dark ink enhances the degree of freedom inspecification of the dot on-off conditions and improves the picturequality, which is worsened by the restriction of ink duty.

In accordance with one preferable application of the print controllerthat specifies the dot on-off conditions of the respective inks based onthe image data and the corresponding method of controlling the printingoperation, the technique specifies the dot on-off conditions with regardto the plurality of basic color inks, which include at least yellow ink,as well as with the dark yellow ink, which has a main wavelength regionof light absorption substantially identical with that of the yellow inkbut a lower lightness than that of the yellow ink. The results of thespecification are output to a printer that enables creation of dots withthe plurality of basic color inks and the dark yellow ink. The printerreceives the specification of the dot on-off conditions and creates dotswith the plurality of basic color inks including at least the yellow inkand with the dark yellow ink, so as to print an image.

The yellow ink has a relatively high lightness. Even the dark yellowink, which is darker than the yellow ink, still has a high lightness, sothat dots of the dark yellow ink are relatively inconspicuous. Creationof dots with the dark yellow ink thus significantly improves the picturequality of the resulting printed image.

In accordance with one preferable application of the print controller ofthe present invention, the dot on-off conditions are specified withregard to at least the cyan ink, the magenta ink, and the yellow ink asthe plurality of basic color inks. In this case, the dark ink may have ahue that is closest to the hue of the yellow ink among the cyan ink, themagenta ink, and the yellow ink. Specification of the dot on-offconditions with regard to the dark ink is carried out to enable dotswith the dark ink to be created together with dots of at least one ofthe basic color inks when an image to be printed has hues varying fromred to green on a Munsell hue circle.

The image having hues varying from red to green on the Munsell huecircle is printed by adequately creating dots of the magenta ink or dotsof the cyan ink together with the dots of the yellow ink. The techniqueof this application enables the image having such hues to bealternatively printed by adequately creating dots of the dark inktogether with the dots of the basic color ink. This arrangementeffectively enhances the degree of freedom in specification of the doton-off conditions with regard to each color ink, thereby improving thepicture quality of the resulting printed image.

In accordance with one preferable application of the print controller ofthe present invention, the dot on-off conditions are specified withregard to at least the cyan ink, the magenta ink, and the yellow ink asthe plurality of basic color inks. In this case, the dark ink may have ahue that is closest to the hue of the yellow ink among the cyan ink, themagenta ink, and the yellow ink. Specification of the dot on-offconditions with regard to the dark ink is carried out to enable dotswith the dark ink to be created prior to creation of dots with eitherone of the cyan ink and the magenta ink when an image to be printed hashues varying from yellow to black.

Dots of the magenta ink or the cyan ink are rather conspicuous in anyellow image, unless the yellow image has a sufficiently low lightness.When an image to be printed has hues varying from yellow to black,creation of dots with the dark ink prior to creation of dots with themagenta ink or the cyan ink lowers the lightness of the image and makesthe dots of the magenta ink or the cyan ink sufficiently inconspicuous.The hue of the dark ink is closest to the hue of the yellow ink.Creation of dots with the dark ink in the yellow image prior to creationof dots with the magenta ink or the cyan ink accordingly does not makethe dots of the dark ink conspicuous to lower the picture quality. Usingthe dark ink having the above characteristics thus preferably improvesthe picture quality of the resulting printed image. The dots of thelight cyan ink, which has the lower density than that of the cyan ink,and the dots of the light magenta ink, which has the lower density thanthat of the magenta ink, are not so conspicuous in an image having arelatively high lightness. Dots of the dark ink may thus be created inan overlapping manner on the dots of the light cyan ink or on the dotsof the light magenta ink. In the case of a variable-dot printer,small-size dots are not so conspicuous even when they are created in animage having a relatively high lightness. Like in the case of the lightink, dots of the dark ink may thus be created in an overlapping manneron the small-size dots of the cyan ink or on the small-size dots of themagenta ink.

In accordance with one preferable application of the print controller ofthe present invention, the dot on-off conditions are specified withregard to at least the cyan ink, the magenta ink, and the yellow ink asthe plurality of basic color inks. In this case, the dark ink may have ahue that is closest to the hue of the yellow ink among the cyan ink, themagenta ink, and the yellow ink, and a lower lightness than that of theyellow ink. Specification of the dot on-off conditions with regard tothe dark ink is carried out to enable dots with the dark ink to becreated prior to creation of dots with either one of the cyan ink andthe magenta ink when an image to be printed has hues varying from colorof the either one of the cyan ink and the magenta ink to black.

Dots of the cyan ink in a magenta image or dots of the magenta ink in acyan image are rather conspicuous, unless the image has a sufficientlylow lightness. When an image to be printed has hues varying from magentato black or hues varying from cyan to black, creation of dots with thedark ink prior to creation of dots with the magenta ink or the cyan inkdesirably lowers the lightness of the image and makes the dots of themagenta ink or the cyan ink sufficiently inconspicuous. The dark ink hasthe hue closest to the hue of the yellow ink. Like the dots of theyellow ink, dots of the dark ink are thus relatively inconspicuous inboth the magenta image and the cyan image. Creation of dots with thedark ink prior to creation of dots with the magenta ink or the cyan inkaccordingly does not make the dots of the dark ink conspicuous to lowerthe picture quality. Using the dark ink having the above characteristicsthus preferably improves the picture quality of the resulting printedimage. The dots of the light cyan ink and the dots of the light magentaink are not so conspicuous in an image having a relatively highlightness. Dots of the dark ink may thus be created in an overlappingmanner on the dots of the light cyan ink or on the dots of the lightmagenta ink. In the case of a variable-dot printer, small-size dots arenot so conspicuous even when they are created in an image having arelatively high lightness. Like in the case of the light ink, dots ofthe dark ink may thus be created in an overlapping manner on thesmall-size dots of the cyan ink or on the small-size dots of the magentaink.

In accordance with one preferable application of the print controller ofthe present invention, the dot on-off conditions are specified withregard to at least the cyan ink, the magenta ink, and the yellow ink asthe plurality of basic color inks. In this case, the dark ink may have ahue that is closest to the hue of the yellow ink among the cyan ink, themagenta ink, and the yellow ink, and a lower lightness than that of theyellow ink. Specification of the dot on-off conditions with regard tothe dark ink is carried out to enable dots with the dark ink to becreated after creation of dots with the yellow ink when an image to beprinted has hues varying from color of either one of the cyan ink andthe magenta ink to black.

Dots of the cyan ink in a magenta image or dots of the magenta ink in acyan image are rather conspicuous, unless the image has a sufficientlylow lightness. Creating yellow dots in such images lowers the lightnessof the image to some extent. The dots of the cyan ink or the magenta inkmay, however, be still rather conspicuous in these images. Thistechnique creates dots with the dark ink subsequent to creation of dotswith the yellow ink. This further lowers the lightness of the image andmakes the dots of the magenta ink or the cyan ink sufficientlyinconspicuous. The dark ink has the hue closest to the hue of the yellowink. Like the dots of the yellow ink, dots of the dark ink are thusrelatively inconspicuous in both the magenta image and the cyan image.Using the dark ink having the above characteristics thus preferablyimproves the picture quality of the resulting printed image.

In accordance with another preferable application of the printcontroller of the present invention, the dot on-off conditions arespecified with regard to the plurality of basic color inks including atleast the cyan ink, the magenta ink, and the yellow ink, as well as withregard to the light ink, which has a hue substantially identical withthe hue of the cyan ink or the magenta ink but a lower density than thatof the cyan ink or the magenta ink. In this case, the dark ink may havea hue that is closest to the hue of the yellow ink among the cyan ink,the magenta ink, and the yellow ink. Specification of the dot on-offconditions with regard to the dark ink is carried out to enable dotswith the dark ink to be created after creation of dots with the lightink when an image to be printed has hues varying from yellow to black.

Dots of the magenta ink or the cyan ink are rather conspicuous in anyellow image, unless the yellow image has a sufficiently low lightness.When an image to be printed has hues varying from yellow to black,formation of dots with the light ink desirably lowers the lightness ofthe image. Formation of dots with the dark ink in addition to with thelight ink further lowers the lightness of the image and thereby makesthe dots of the magenta ink and the cyan ink more inconspicuous. The hueof the dark ink is closest to the hue of the yellow ink. The dots of thedark ink are thus inconspicuous in the yellow image and do not lower thepicture quality. Using the dark ink having the above characteristicsthus preferably improves the picture quality of the resulting printedimage.

The light ink, whose dot on-off conditions are specified by the printcontroller, may be light cyan ink having a hue substantially identicalwith that of the cyan ink but a lower density than that of the cyan inkor light magenta ink having a hue substantially identical with that ofthe magenta ink but a lower density than that of the magenta ink. Dotsof the dark ink may be created after creation of dots with these lightinks. More specifically dots of the dark ink may be created aftercreation of dots with both the light cyan ink and the light magenta ink.

Creating dots with these light inks lowers the lightness in an yellowimage. Creating dots with the dark ink further lowers the lightness inthe yellow image. This makes the dots of the cyan ink and the magentaink more inconspicuous and improves the picture quality of the resultingprinted image.

In accordance with one preferable application of the print controllerthat specifies the dot on-off conditions of the respective inks based onthe image data and the corresponding method of controlling the printingoperation, the technique specifies dot on-off conditions with regard toa plurality of basic color inks, which include at least cyan ink,magenta ink, and yellow ink, as well as with dark yellow ink, which hasa main wavelength region of light absorption substantially identicalwith that of the yellow ink but a lower lightness than that of theyellow ink. The results of the specification are output to a printerthat enables creation of dots with the plurality of basic color inks andthe dark yellow ink. The printer receives the specification of the doton-off conditions and creates dots with the plurality of basic colorinks including at least the cyan ink, the magenta ink, and the yellowink and with the dark yellow ink, so as to print an image.

The yellow ink has a relatively high lightness. Even the dark yellowink, which is darker than the yellow ink, still has a higher lightnessthan those of the cyan ink and the magenta ink. Dots of the dark yellowink are accordingly not so conspicuous as dots of the cyan ink or themagenta ink. Using the dark yellow ink in addition to the cyan ink,magenta ink, and the yellow ink to create dots and print an image thussignificantly improves the picture quality of the resulting printedimage.

The printing apparatus of the present invention applicable to theprinting system discussed above may have another arrangement. Thepresent invention is accordingly directed to a printing apparatus thathas a print head to create dots with a plurality of different inks on aprinting medium, receives control information to control the creation ofdots with the plurality of different inks, and actually creates dotswith the plurality of different inks, based on the input controlinformation, so as to print an image. The printing apparatus includes: abasic color ink supply unit that supplies a plurality of basic colorinks to the print head, the plurality of basic color inks being combinedwith one another to express achromatic color; a dark ink supply unitthat supplies a dark ink to the print head, the dark ink having a mainwavelength region of light absorption substantially identical with thatof one basic color ink selected out of the plurality of basic color inksbut a lower lightness than that of the selected basic color ink; acontrol information input unit that receives the control informationwith regard to dots of the plurality of basic color inks and the darkink; and a dot formation unit that drives the print head based on theinput control information, so as to create dots with the plurality ofbasic color inks and the dark ink.

The present invention is also directed to a method of printing, whichcorresponds to the printing apparatus of the above configuration. Thepresent invention thus provides a method of receiving controlinformation to control creation of dots with a plurality of differentinks and driving a print head, which creates dots with the plurality ofdifferent inks on a printing medium, based on the control information,so as to print an image. The method includes the steps of: (a) supplyinga plurality of basic color inks and a dark ink to the print head, theplurality of basic color inks being combined with one another to expressachromatic color, the dark ink having a main wavelength region of lightabsorption substantially identical with that of one basic color inkselected out of the plurality of basic color inks but a lower lightnessthan that of the selected basic color ink; (b) receiving the controlinformation with regard to dots of the plurality of basic color inks andthe dark ink; and (c) driving the print head based on the input controlinformation to create dots with the plurality of basic color inks andthe dark ink, thereby printing an image.

In the printing apparatus of the present invention and the correspondingmethod of printing, the print head is driven according to the inputcontrol information for controlling creation of dots with regard to theplurality of basic color inks and the dark ink. Dots with the pluralityof basic color inks and the dark ink are then created on the printingmedium to print an image.

The use of the dark ink in addition to the plurality of basic color inksenhances the degree of freedom in specification of dot on-off conditionsand thus enables the adequate specification of the dot on-offconditions. The supplies of the plurality of basic color inks and thedark ink are fed to the print head, and the print head is then drivenaccording to the results of the specification of the dot on-offconditions. This arrangement enables the dots to be adequately formedwith the respective inks on a printing medium, so as to print an imageof high picture quality.

In accordance with one preferable application of the present invention,the printing apparatus creates dots with at least cyan ink, magenta ink,and yellow ink as the dots with the plurality of basic color inks.

The creation of dots with at least the cyan ink, the magenta ink, andthe yellow ink enables expression of a practically sufficient number ofhues. The use of the dark ink in addition to these various color inksenhances the degree of freedom in specification of dot on-off conditionsand thereby improves the picture quality of the resulting printed image.

In accordance with another preferable application of the presentinvention, the printing apparatus creates dots with at least black inkin addition to the cyan ink, the magenta ink, and the yellow ink. Theprinting apparatus also creates dots with dark yellow ink, which has amain wavelength region of light absorption substantially identical withthat of the yellow ink but a lower lightness than that of the yellowink.

Creation of dots with the black ink in addition to the cyan ink, themagenta ink, and the yellow ink further improves the picture quality ofthe resulting printed image. The use of the dark yellow ink in additionto these inks enhances the degree of freedom in specification of the doton-off conditions and thereby improves the picture quality of theresulting printed image.

In accordance with another preferable application of the presentinvention, the printing apparatus creates dots with at least cyan ink,magenta ink, and yellow ink as the plurality of basic color inks, aswell as with the dark ink and at least one light ink, which has a huesubstantially identical with that of at least one basic color inkselected out of the plurality of basic color inks but a lower densitythan that of the at least one basic color ink.

Creation of dots with the variety of color inks including the light inkimproves the picture quality of the resulting printed image. The use ofthe dark ink in addition to these various color inks enhances the degreeof freedom in specification of the dot on-off conditions and therebyfurther improves the picture quality of the resulting printed image.

In accordance with sill another preferable application of the presentinvention, the printing apparatus creates at least two variable-sizedots having different sizes with regard to at least cyan ink, magentaink, and yellow ink as the plurality of basic color inks.

Creation of the at least two variable-size dots with regard to therespective inks improves the picture quality of the resulting printedimage. The use of the dark ink in addition to these inks enhances thedegree of freedom in specification of the dot on-off conditions andthereby further improves the picture quality of the resulting printedimage.

In accordance with another preferable application of the presentinvention, the printing apparatus has an ink reservoir unit, in whichthe plurality of basic color inks and the dark ink are keptindependently.

In the printing apparatus having the ink reservoir unit forindependently keeping the plurality of basic color inks and the darkink, supplies of the respective inks from the ink reservoir unit to theprint head cause dots of the plurality of basic color inks and dots ofthe dark ink to be created on the printing medium. This results inprinting an image of high picture quality. The arrangement of keepingthe respective inks independently means that the respective inks shouldbe accommodated in a non-miscible manner. These inks may be kepttogether in one ink reservoir unit or may be kept separately indifferent ink reservoir unit.

In this printing apparatus, the ink reservoir unit may keep a greaterquantity of the dark ink than a quantity of the one basic color inkcorresponding to the dark ink.

When natural images, such as landscapes and portraits, are printed, agreater quantity of the dark ink is generally consumed than the quantityof the basic color ink having the closest hue to that of the dark ink.The ink reservoir unit keeping the greater quantity of the dark ink thanthe quantity of the corresponding basic color ink thus favorably causesthe quantities of the respective inks kept in the ink reservoir unit tobe close to the actual quantities of ink consumption.

In accordance with one preferable application of the printing apparatusof the present invention and the corresponding method of printing, theprint head is driven according to the input control information tocreate dots with the respective inks, wherein the control informationcontrols creation of dots with the plurality of basic color inks, whichinclude at least cyan ink, magenta ink, and yellow ink, as well as withdark yellow ink, which has a main wavelength region of light absorptionsubstantially identical with that of the yellow ink but a lowerlightness than that of the yellow ink.

In the printing apparatus of this arrangement and the correspondingmethod of printing, dots are created with the dark yellow ink as well aswith the cyan ink, the magenta ink, and the yellow ink. This arrangementenhances the degree of freedom in specification of dot on-off conditionsand thereby improves the picture quality of the resulting printed image.

In accordance with one preferable application of the present invention,the printing apparatus has an ink reservoir unit that keeps at least thecyan ink, the magenta ink, the yellow ink, and the dark yellow inkindependently. The ink reservoir unit keeps a greater quantity of thedark yellow ink than a quantity of the yellow ink.

When natural images, such as landscapes and portraits, are printed, agreater quantity of the dark yellow ink is generally consumed than thequantity of the yellow ink. The ink reservoir unit keeping the greaterquantity of the dark yellow ink than the quantity of the yellow ink thusfavorably causes the quantities of the respective inks kept in the inkreservoir unit to be close to the actual quantities of ink consumption.

The technique of the present invention may be implemented by a computer,which reads a specific program that actualizes the functions of theprinting system, the print controller, or the printing apparatus of thepresent invention discussed above. One application of the presentinvention is a recording medium, in which a specific program forattaining the functions of the printing system of the present inventionis recorded. The present invention is thus directed to a recordingmedium, in which a specific program is recorded in a computer readablemanner. The specific program actualizes a method of creating dots with aplurality of different inks, so as to print an image on a printingmedium. The specific program causes a computer to attain the functionsof: specifying dot on-off conditions with regard to a plurality of basiccolor inks and a dark ink based on input image data, the plurality ofbasic color inks being combined with one another to express achromaticcolor, the dark ink having a main wavelength region of light absorptionsubstantially identical with that of one basic color ink selected out ofthe plurality of basic color inks but a lower lightness than that of theselected basic color ink; and controlling creation of dots with theplurality of basic color inks and the dark ink, based on thespecification of the dot-on-off conditions with regard to the pluralityof basic color inks and the dark ink.

Another application of the present invention is a recording medium, inwhich a specific program for attaining the functions of the printcontroller of the present invention is recorded. The present inventionis thus directed to another recording medium, in which a specificprogram is recorded in a computer readable manner. The specific programactualizes a method of supplying control information to a printer, whichcreates dots with a plurality of different inks on a printing medium, inorder to control the creation of dots with the plurality of differentinks and thereby controlling a printing operation of the printer. Thespecific program causes a computer to attain the functions of:specifying dot on-off conditions with regard to a plurality of basiccolor inks and a dark ink based on input image data, the plurality ofbasic color inks being combined with one another to express achromaticcolor, the dark ink having a main wavelength region of light absorptionsubstantially identical with that of one basic color ink selected out ofthe plurality of basic color inks but a lower lightness than that of theselected basic color ink; and outputting the specification of the doton-off conditions with regard to the plurality of basic color inks andthe dark ink to the printer as the control information, so as to controlthe printing operation of the printer.

Still another application of the present invention is a recordingmedium, in which a specific program for attaining the functions of theprinting apparatus of the present invention is recorded. The presentinvention is thus directed to a recording medium, in which a specificprogram is recorded in a computer readable manner. The specific programactualizes a method of receiving control information to control creationof dots with a plurality of different inks and driving a print head,which creates dots with the plurality of different inks on a printingmedium, based on the control information, so as to print an image. Thespecific program causes a computer to attain the functions of: receivingthe control information to control creation of dots with a plurality ofbasic color inks and a dark ink, the plurality of basic color inks beingcombined with one another to express achromatic color, the dark inkhaving a main wavelength region of light absorption substantiallyidentical with that of one basic color ink selected out of the pluralityof basic color inks but a lower lightness than that of the selectedbasic color ink; and driving the print head based on the input controlinformation to create dots with the plurality of basic color inks andthe dark ink, thereby printing an image.

The computer reads any one of the specific programs recorded in therecording media to actualize the respective functions. Creation of dotswith the dark ink as well as with the plurality of basic color inksimproves the picture quality of the resulting printed image.

In accordance with one preferable application of the present invention,the specific program recorded in the recording medium for attaining thefunctions of the print controller further causes the computer to attainthe function of storing in advance mappings of tints used to express acolor image to combinations of the plurality of basic color inks and thedark ink to represent the tints. In this structure, the dot on-offconditions with regard to the plurality of basic color inks and the darkink are specified, based on the mappings stored in advance. Thisarrangement ensures the quick and accurate specification of the doton-off conditions.

The plurality of basic color inks generally include the cyan ink, themagenta ink, and the yellow ink. It is preferable that the dark ink hasa hue close to the hue of the yellow ink, which has the highestlightness among these basic color inks. There is accordingly anotherpossible application of the recording medium, in which a specificprogram for attaining the functions of the print controller is recorded.The present invention is thus directed to a recording medium, in which aspecific program is recorded in a computer readable manner. The specificprogram actualizes a method of supplying control information to aprinter, which creates dots with a plurality of different inks on aprinting medium, in order to control the creation of dots with theplurality of different inks and thereby controlling a printing operationof the printer. The specific program causes a computer to attain thefunctions of: specifying dot on-off conditions with regard to aplurality of basic color inks and dark yellow ink based on input imagedata, the plurality of basic color inks including at least cyan ink,magenta ink, and yellow ink, the dark yellow ink having a mainwavelength region of light absorption substantially identical with thatof the yellow ink but a lower lightness than that of the yellow ink; andoutputting the specification of the dot on-off conditions with regard tothe plurality of basic color inks and the dark yellow ink to the printeras the control information, so as to control the printing operation ofthe printer.

There is also another possible application of the recording medium, inwhich a specific program for attaining the functions of the printingapparatus is recorded. The present invention is thus directed to arecording medium, in which a specific program is recorded in a computerreadable manner. The specific program actualizes a method of receivingcontrol information to control creation of dots with a plurality ofdifferent inks and driving a print head, which creates dots with theplurality of different inks on a printing medium, based on the controlinformation, so as to print an image. The specific program causes acomputer to attain the functions of: receiving the control informationto control creation of dots with a plurality of basic color inks anddark yellow ink, the plurality of basic color inks including at leastcyan ink, magenta ink, and yellow ink, the dark yellow ink having a mainwavelength region of light absorption substantially identical with thatof the yellow ink but a lower lightness than that of the yellow ink; anddriving the print head based on the input control information to createdots with the plurality of basic color inks and the dark yellow ink,thereby printing an image.

The computer reads the specific program recorded in the recording mediumto actualize the respective functions, so as to create dots with atleast the cyan ink, the magenta ink, the yellow ink, and the dark yellowink. This arrangement enables an image of high picture quality to beprinted.

In the printing apparatus of the present invention, the dark ink issupplied by the dark ink supply unit. Other possible applications of thepresent invention are accordingly ink cartridges, in which the dark iskept. The present invention is thus directed to an ink cartridgedetachably attached to a printing apparatus, which prints an image witha plurality of basic color inks, wherein the plurality of basic colorinks are combined with one another to express achromatic color. The inkcartridge keeps therein at least one ink to be supplied to the printingapparatus. The ink cartridge has an ink reservoir that keeps therein adark ink, the dark ink having a main wavelength region of lightabsorption substantially identical with that of one basic color inkselected out of the plurality of basic color inks but a lower lightnessthan that of the selected basic color ink.

Attachment of this ink cartridge to the printing apparatus enables theprinting apparatus to create dots with the dark ink. As describedpreviously, this arrangement enhances the degree of freedom inspecification of the dot on-off conditions and improves the picturequality of the resulting printed image.

In accordance with one preferable application of the present invention,the dark ink kept in the ink cartridge has lower lightness andsaturation than those of one basic color ink selected out of theplurality of basic color inks.

In accordance with another preferable application of the presentinvention, the dark ink kept in the ink cartridge has a main wavelengthregion for most strongly absorbing a ray in a visible range, which issubstantially identical with that of one basic color ink selected out ofthe plurality of basic color inks, and a greater integral of lightabsorptivity in a wavelength region of the visible range than that ofthe selected basic color ink.

In accordance with still another preferable application of the presentinvention, the dark ink kept in the ink cartridge has:

(A) a characteristic wavelength region for strongly absorbing a ray in avisible range to mainly determine the hue of the dark ink, which issubstantially identical with a characteristic wavelength region of onebasic color ink selected out of the plurality of basic color inks;

(B) a mean value of light absorptivity that is greater than orsubstantially identical with a mean value of light absorptivity of theselected basic color ink in the characteristic wavelength region of thedark ink; and

(C) a mean value of light absorptivity that is greater than a mean valueof light absorptivity of the selected basic color ink in a wavelengthregion of visible light except the characteristic wavelength region ofthe dark ink.

Attachment of the ink cartridge, in which any one of these dark inks iskept, to the printing apparatus enables the printing apparatus to createdots with the dark ink. This arrangement improves the picture quality ofthe resulting printed image.

In accordance with one preferable application of the present invention,the ink cartridge further keeps therein one basic color ink selected outof the plurality of basic color inks. In accordance with anotherpreferable application of the present invention, the ink cartridgefurther keeps therein black ink, which is achromatic and has a lowlightness. In accordance with still another preferable application ofthe present invention, the ink cartridge further keeps therein at leastone light ink, which has a hue substantially identical with that of atleast one basic color ink selected out of the plurality of basic colorinks but a lower density than that of the at least one basic color ink.

The arrangement of keeping any of these inks in addition to the dark inkin the same ink cartridge saves the total space required for the inkcartridges, compared with separate ink cartridges that independentlykeep one of these inks therein.

In accordance with another preferable application of the presentinvention, the ink cartridge further keeps therein one basic color inkselected out of the plurality of basic color inks and at least one lightink, which has a hue substantially identical with that of at least onebasic color ink selected out of the plurality of basic color inks but alower density than that of the at least one basic color ink. Thearrangement of keeping these inks together in addition to the dark inkin the same ink cartridge further saves the total space required for theink cartridges. These color inks including the dark ink are mainlyconsumed in the process of printing a color image, whereas the black inkis mainly consumed in the process of printing a black and white image,for example, a document. The arrangement keeps these color inks, whichare mainly consumed to print a color image, together in the same inkcartridge, separate from the black ink. This arrangement desirablyenables only the ink cartridge keeping inks mainly consumed to bereplaced according to the image to be printed.

The ink cartridge of the present invention may keep therein an inkhaving the following characteristics as the dark ink:

(A) a characteristic wavelength region that is mostly in a wavelengthrange of 400 nm to 500 nm, the characteristic wavelength region stronglyabsorbing a ray in a visible range to mainly determine the hue of thedark yellow ink; and

(B) a mean value of absorptivity of the ray in the visible range exceptthe characteristic wavelength region, which ranges from 10% to 60%.

The ink cartridge of the present invention may alternatively keeptherein an ink having the following characteristics as the dark ink:

(A) a hue included in a specific range of 10R to 10GY on a Munsell huecircle; and

(B) a saturation of smaller than 3.5C on a Munsell chroma.

Attachment of the ink cartridge, in which any of these inks is kept, tothe printing apparatus enables the printing apparatus to create dotswith the dark ink. This arrangement improves the picture quality of theresulting printed image.

The present invention is directed to an ink cartridge that keeps thereinyellow ink and dark yellow ink, which has a lower lightness than that ofthe yellow ink. The present invention is also directed to an inkcartridge that keeps therein dark yellow ink and black ink. The presentinvention is further directed to an ink cartridge that keeps thereinyellow ink, dark yellow ink, cyan ink, light cyan ink, magenta ink, andlight magenta ink.

The arrangement of keeping these inks together in the same ink cartridgesaves the total space required for the ink cartridges, compared withseparate ink cartridges that independently keep one of these inkstherein.

In accordance with one preferable application of the ink cartridge, thecapacity of the dark yellow ink may be set to be greater than thecapacity of the yellow ink. When a natural image, such as a landscape ora portrait, is printed, the consumption of the dark yellow ink tends tobe greater than the consumption of the yellow ink. The greater capacityof the dark yellow ink than that of the yellow ink thus enables thesetwo inks to be used up at substantially the same time. This arrangementdesirably reduces the waste of ink by a replacement of the inkcartridge, in which one ink is used up but a large quantity of the otherink still remains.

The present invention is also directed to an ink cartridge that keepstherein dark yellow ink, light cyan ink and light magenta ink. Thearrangement of keeping these inks together in the same ink cartridgesaves the total space required for the ink cartridges, compared withseparate ink cartridges that independently keep one of these inkstherein. When a natural image, such as a landscape or a portrait, isprinted, these inks are often consumed more than the other inks. Thearrangement of keeping the dark yellow ink the light cyan ink, and thelight magenta ink in the same ink cartridge enables only this inkcartridge to be replaced according to the image to be printed.

In accordance with one preferable application of the present invention,the ink cartridge further has a storage device that stores informationregarding a quantity of each ink kept therein in a readable, writable,and volatile manner.

Storing the information regarding the quantity of each ink kept in theink cartridge ensures the printing operation based on the informationwith regard to the accurate remaining quantity of ink. This arrangementeffectively prevents the ink from being used up in the course ofprinting.

The storage device included in the ink cartridge may have an inkquantity information storage area, which is accessed to be written firstby the printing apparatus and in which the information regarding thequantity of each ink kept in the ink cartridge is stored.

The area written first is, for example, a head area in the storagedevice or any area in the storage device accessible to be written firstby the printing apparatus. Storing the information regarding thequantity of each ink in this area shortens the time required for writingthe information. This arrangement effectively prevents the informationto be written from being destroyed by cutting off the power supply ofthe printing apparatus in the course of the writing operation.

When the dark ink kept in the ink cartridge is used up, an ink supplieris used to feed a supply of the dark ink to the ink cartridge, so as tocontinue creation of dots with the dark ink and print an image of highquality. Another application of the present invention is accordingly anink supplier. The present invention is thus directed to an ink supplierthat feeds a supply of ink to an ink cartridge, wherein the inkcartridge is detachably attached to a printing apparatus and keepstherein at least one ink used by the printing apparatus. The inksupplier includes a sealed ink reservoir that keeps an ink in a sealingmanner, and an ink supply unit that feeds a supply of the sealed ink tothe ink cartridge. The ink sealed in the sealed ink reservoir has thefollowing characteristics:

(A) a characteristic wavelength region that is mostly included in awavelength range of 400 nm to 500 nm, the characteristic wavelengthregion strongly absorbing a ray in a visible range to mainly determinethe hue of the ink; and

(B) a mean value of absorptivity of the ray in the visible range exceptthe characteristic wavelength region, which ranges from 10% to 60%.

The ink supplier has the sealed ink reservoir that keeps an ink in asealing manner, and the ink supply unit that feeds a supply of thesealed ink to the ink cartridge. The ink having the abovecharacteristics (A) and (B) is sealed in the sealed ink reservoir. Thecharacteristic wavelength region of the ink, which mainly determines thehue of the ink, is mostly included in the wavelength range of 400 nm to500 nm. This means that the ink roughly has the hue of yellow. The inkhas the mean value of absorptivity of the ray in the visible rangeexcept the characteristic wavelength region, which ranges from 10% to60%. This means that the ink has a low lightness. The ink having thecharacteristics (A) and (B) is accordingly replaceable with the darkink. In the event that the dark ink kept in the ink cartridge is usedup, supply of the ink from the ink supplier to the ink cartridge enablescontinuous creation of dots with the dark ink to print an image of highpicture quality.

The ink sealed in the ink supplier may alternatively have the followingcharacteristics:

(A) a hue included in a specific range of 10R to 10GY on a Munsell huecircle; and

(B) a saturation of smaller than 3.5C on a Munsell chroma.

This ink may also be used as the dark ink. A supply of this ink sealedin the ink supplier to the ink cartridge enables creation of dots withthe dark ink.

The technique of the present invention may be implemented by a programcode that is stored in a computer to attain the functions of theprinting system, the print controller, or the printing apparatus of thepresent invention discussed above. The computer then executes therespective functions written in the program code. A first possibleapplication of the present invention is thus a program code, in which amethod of creating dots with a plurality of different inks so as toprint an image on a printing medium is written in a computer readablemanner. The method actualizes the functions of: specifying dot on-offconditions with regard to a plurality of basic color inks and a dark inkbased on input image data, the plurality of basic color inks beingcombined with one another to express achromatic color, the dark inkhaving a main wavelength region of light absorption substantiallyidentical with that of one basic color ink selected out of the pluralityof basic color inks but a lower lightness than that of the selectedbasic color ink; and controlling creation of dots with the plurality ofbasic color inks and the dark ink, based on the specification of thedot-on-off conditions with regard to the plurality of basic color inksand the dark ink.

A second possible application of the present invention is a programcode, in which a method of supplying control information to a printer,which creates dots with a plurality of different inks on a printingmedium, in order to control the creation of dots with the plurality ofdifferent inks and thereby controlling a printing operation of theprinter is written in a computer readable manner. The method actualizesthe functions of: specifying dot on-off conditions with regard to aplurality of basic color inks and a dark ink based on input image data,the plurality of basic color inks being combined with one another toexpress achromatic color, the dark ink having a main wavelength regionof light absorption substantially identical with that of one basic colorink selected out of the plurality of basic color inks but a lowerlightness than that of the selected basic color ink; and outputting thespecification of the dot on-off conditions with regard to the pluralityof basic color inks and the dark ink to the printer as the controlinformation, so as to control the printing operation of the printer.

A third possible application of the present invention is a program code,in which a method of receiving control information to control creationof dots with a plurality of different inks and driving a print head,which creates dots with the plurality of different inks on a printingmedium, based on the control information, so as to print an image iswritten in a computer readable manner. The method actualizes thefunctions of: receiving the control information to control creation ofdots with a plurality of basic color inks and a dark ink, the pluralityof basic color inks being combined with one another to expressachromatic color, the dark ink having a main wavelength region of lightabsorption substantially identical with that of one basic color inkselected out of the plurality of basic color inks but a lower lightnessthan that of the selected basic color ink; and driving the print headbased on the input control information to create dots with the pluralityof basic color inks and the dark ink, thereby printing an image.

Any of the print controllers and the printing apparatuses of the presentinvention discussed above may provide a plurality of dark inks and usesa most suitable dark ink or the plurality of dark inks simultaneouslyaccording to an image to be printed. The present invention mayaccordingly have other possible applications discussed below. A fourthpossible application of the present invention is thus a print controllerthat supplies control information to a printer, which creates dots witha plurality of different inks, in order to control the creation of dotswith the plurality of different inks. The printer creates dots with aplurality of basic color inks as well as with a plurality of dark inks,wherein the plurality of basic color inks are combined with one anotherto express achromatic color, and each of the dark inks has a mainwavelength region of light absorption substantially identical with thatof one basic color ink selected out of the plurality of basic color inksbut a lower lightness than that of the selected basic color ink. Theprint controller includes: a dot on-off condition specification unitthat specifies dot on-off conditions with regard to the plurality ofbasic color inks and the plurality of dark inks, based on input imagedata; and a control information output unit that outputs thespecification of the dot on-off conditions with regard to the pluralityof basic color inks and the plurality of dark inks to the printer as thecontrol information.

A fifth possible application of the present invention is a printingapparatus that has a print head to create dots with a plurality ofdifferent inks on a printing medium, receives control information tocontrol the creation of dots with the plurality of different inks, andactually creates dots with the plurality of different inks, based on theinput control information, so as to print an image. The printingapparatus includes: a basic color ink supply unit that supplies aplurality of basic color inks to the print head, wherein the pluralityof basic color inks are combined with one another to express achromaticcolor; a dark ink supply unit that supplies a plurality of dark inks tothe print head, wherein each of the dark inks has a main wavelengthregion of light absorption substantially identical with that of onebasic color ink selected out of the plurality of basic color inks but alower lightness than that of the selected basic color ink; a controlinformation input unit that receives the control information with regardto dots of the plurality of basic color inks and the plurality of darkinks; and a dot formation unit that drives the print head based on theinput control information, so as to create dots with the plurality ofbasic color inks and the plurality of dark inks.

These and other objects, features, aspects, and advantages of thepresent invention will become more apparent from the following detaileddescription of the preferred embodiment with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram schematically illustrating the structure of aprinting system including a print controller and a color printer in oneembodiment according to the present invention;

FIG. 2 is a block diagram illustrating a software configuration of theprinting system of the embodiment;

FIG. 3 schematically illustrates the structure of the color printer ofthe embodiment;

FIGS. 4A and 4B show the principle of dot formation in the color printerof the embodiment;

FIGS. 5A and 5B show arrangements of nozzles in the color printer of theembodiment;

FIG. 6 shows the internal structure of the print controller of theembodiment;

FIG. 7 shows a process of receiving data output from a print head to adrive buffer and creating dots in the printing system of the embodiment;

FIGS. 8A through 8F are perspective views showing ink cartridgesattachable to the color printer of the embodiment;

FIGS. 9A and 9B are graphs showing observed quantities of inkconsumption when natural images are printed with the color printer ofthe embodiment;

FIG. 10 is an enlarged view illustrating a storage element mounted onthe side face of the ink cartridge;

FIG. 11 shows the contents of data stored in the storage element of theink cartridge;

FIG. 12 shows an example of ink compositions used in the color printerof the embodiment;

FIG. 13 is a graph showing the curves of lightness with regard to therespective inks having the compositions shown in FIG. 12;

FIGS. 14A through 14E are graphs conceptually showing the spectroscopiccharacteristics of the respective color inks used in the color printerof the embodiment;

FIG. 15 is a graph showing the spectroscopic characteristics of darkyellow ink that is designed by utilizing the degree of freedom inspectroscopic settings in a wavelength region of longer than 650 nm;

FIG. 16 shows expression of colors with dots of dark yellow ink on asheet of printing paper;

FIG. 17 schematically illustrates the appearance of an ink supplier usedto feed a supply of ink to the ink cartridge;

FIG. 18 is a flowchart showing an image processing routine executed inthe embodiment;

FIG. 19 shows a conversion table used in the embodiment;

FIGS. 20A and 20B conceptually show a method of determining the rate offormation of dark ink dots in the embodiment;

FIGS. 21A and 21B show a binarization process;

FIG. 22 is a flowchart showing a binarization process by the errordiffusion method executed in the embodiment;

FIG. 23 shows an example of weights added in the process of diffusingthe error by the error diffusion method;

FIG. 24 shows the systematic dither method;

FIGS. 25A, 25B, and 25C show results of simulative computation of thedot recording ratio with regard to each color ink in the case ofprinting a gradation pattern from red to black with the color printer ofthe embodiment;

FIGS. 26A, 26B, and 26C show results of simulative computation of thedot recording ratio with regard to each color ink in the case ofprinting a gradation pattern from magenta to black with the colorprinter of the embodiment;

FIGS. 27A, 27B, and 27C show results of simulative computation of thedot recording ratio with regard to each color ink in the case ofprinting a gradation pattern from white to black with the color printerof the embodiment;

FIGS. 28A, 28B, and 28C show results of simulative computation of thedot recording ratio with regard to each color ink in the case ofprinting a gradation pattern from red to black with the color printerusing only the four color inks C, M, Y, and K; and

FIGS. 29A and 29B show results of simulative computation of the dotrecording ratio with regard to each color ink in the case of printing agradation pattern from white to black with the color printer using onlythe three color inks C, M, and Y.

DESCRIPTION OF THE PREFERRED EMBODIMENT

One mode for carrying out the present invention is described below inthe following sequence as a preferred embodiment:

A. Structure of Apparatus

A-1. General Structure

A-2. Structure of Ink Cartridge

A-3. Dark Yellow Ink

B. Image Processing

B-1. Process of Converting Resolution

B-2. Color Conversion Process

B-3. Process of Converting Number of Tones

B-4. Binarization by Error Diffusion Method

B-5. Binarization by Systematic Dither Method

B-6. Interlace Process

C. Results of Simulations

C-1. Gradation Pattern from Red to Black

C-2. Gradation Pattern from Magenta to Black

C-3. Gradation Pattern from White to Black

C-4. Application to Printer with Four Color Inks

C-5. Application to Printer with Three Color Inks

A. Structure of Apparatus

A-1. General Structure

FIG. 1 is a block diagram schematically illustrating the structure of aprinting system including a print controller and a printing apparatus inone embodiment according to the present invention. FIG. 2 is a blockdiagram illustrating a software configuration of the printing system ofthe embodiment. The printing system includes a computer 80 connected toa color printer 20 and a color scanner 21. The computer 80 reads andexecutes predetermined programs to function, in combination with thecolor printer 20 and the color scanner 21, as the printing system as awhole. The color scanner 21 converts a color original, that is, anobject to be printed, into color image data ORG, which are in aprocessible form by the computer 80 and input into the computer 80. Thecomputer 80 carries out required image processing and further convertsthe color image data ORG into image data FNL, which are in a printableform by the printer 20 and input into the color printer 20. The imagedata processible by the computer 80 include those representing imagesread by the color scanner 21 with or without subsequent processing, aswell as those representing images generated by a variety of applicationprograms 91 on the computer 80. The color printer 20 creates dots ofvarious color inks on a sheet of printing paper based on the input imagedata FNL. The series of this procedure enables a resulting color imagecorresponding to the color image data output from the computer 80 to beprinted on the printing paper.

The computer 80 includes a CPU 81 that carries out a variety ofoperations, a ROM 82, a RAM 83, an input interface 84, an outputinterface 85, a CRT controller (CRTC) 86, a disk controller (DDC) 87,and a serial input-output interface (SIO) 88, which are mutuallyconnected via a bus 89 to allow transmission of data. The CRTC 86controls output of signals to a color display CRT 23. The DDC 87controls data transmission to and from a flexible disk drive 25, a harddisk 26, and a CD-ROM drive (not shown). A variety of programs loaded tothe RAM 83 and executed by the CPU 81 and a variety of programs providedin the form of device drivers are stored in the ROM 82 and the hard disk26. Connection of the SIO 88 with a public telephone network PNT via amodem 24 enables required data and programs to be downloaded to the harddisk 26 from a serer SV on an external network.

A supply of power to the computer 80 activates the operating systemstored in the ROM 82 and the hard disk 26 and a variety of applicationprograms 91 under the control of the operating system.

The color printer 20 of this embodiment is a color ink jet printer thatforms dots of seven different color inks, that is, cyan, light cyan,magenta, light magenta, yellow, dark yellow, and black inks, on a sheetof printing paper and thereby prints a color image. The ink jet printerapplied in this embodiment uses piezoelectric elements PE to eject inkas discussed later. The printer may, however, have a print head thatejects ink by another technique, for example, by means of bubbles thatare generated in an ink conduit by a supply of electricity to a heaterdisposed in the ink conduit.

In color printers driven by other principles, for example, laserprinters and thermal transfer printers, there is no fear of tearing orrumpling the printing medium. Application of a large quantity of ink onthe printing medium may, however, cause problems of ink blot andpeel-off. The technique of the embodiment discussed below may thus beapplicable to such color printers.

Referring to FIG. 2, in the computer 80, all the application programs 91work under the control of the operating system. A video driver 90 and aprinter driver 92 are incorporated in the operating system, and imagedata output from each application program 91 are output to the colorprinter 20 via the printer driver 92. The application program 91 thatprocesses an input image, for example, by retouch causes the input imagetaken from the color scanner 21 to be displayed on the CRT 23 via thevideo driver 90. This enables the user to carry out the required imageprocessing while checking the displayed image on the CRT 23.

When the application program 91 issues a print instruction, the printerdriver 92 of the computer 80 receives image data from the applicationprogram 91 and carries out predetermined image processing to convert theinput image data to image data FNL that are printable by the printer 20.As shown conceptually in FIG. 2, the image processing carried out in theprinter driver 92 is mainly classified into four modules, that is, aresolution conversion module 93, a color conversion module 94, ahalftone module 95, and an interlace module 96. The details of the imageprocessing carried out by each module will be discussed later. The imagedata received by the printer driver 92 are subjected to the imageprocessing performed by the respective modules and are output as thefinal image data FNL to the color printer 20. The color printer 20 ofthis embodiment does not carry out the image processing but simplycreates dots according to the input image data FNL. A modifiedapplication may, however, cause the color printer 20 to carry out partof the image processing.

FIG. 3 schematically illustrates the structure of the color printer 20in this embodiment. The color printer 20 has a mechanism of driving aprint head 41 mounted on a carriage 40 to implement ink ejection and dotcreation, a mechanism of moving the carriage 40 forward and backwardalong an axis of a platen 36 by means of a carriage motor 30, amechanism of feeding a sheet of printing paper P by means of a sheetfeed motor 35, and a control circuit 60. The mechanism of reciprocatingthe carriage 40 along the axis of the platen 36 includes a sliding shaft33 that slidably holds the carriage 40 arranged in parallel with theaxis of the platen 36, a pulley 32 that is linked with the carriagemotor 30 via an endless drive belt 31 spanned therebetween, and aposition sensor 34 that detects the position of the origin of thecarriage 40. The mechanism of feeding the printing paper P includes theplaten 36, the sheet feed motor 35 that rotates the platen 36, asheet-feed assist roller (not shown), and a gear train (not shown) thattransmits the rotation of the sheet feed motor 35 to the platen 36 andthe sheet-feed assist roller. The control circuit 60 transmits signalsto and from a control panel 59 of the printer 20 and adequately controlsthe operations of the sheet feed motor 35, the carriage motor 30, andthe print head 41. The sheet of printing paper P fed to the colorprinter 20 is held between the platen 36 and the sheet-feed assistroller and fed by a predetermined length according to a rotational angleof the platen 36.

Ink cartridges 42 and 43 are detachably attached to the carriage 40. Inone example, the ink cartridge 42 has only black (K) ink kept therein,whereas the ink cartridge 43 has a total of six different color inks,three basic color inks, that is, cyan (C), magenta (M), and yellow (Y)inks, as well as three additional color inks, that is, light cyan (LC),light magenta (LM), and dark yellow (DY) inks, kept therein. Namely thecolor printer 20 has dark ink in addition to the standard ink withregard to yellow, and light ink in addition to the standard ink withregard to cyan and magenta.

The combination of these inks may be changed. For example, the darkyellow (DY) ink, the light cyan (LC) ink, and the light magenta (LM) inkmay be kept in one ink cartridge. In another example, only the darkyellow (DY) ink may be kept in a separate ink cartridge. The structuresof these ink cartridges will be discussed in detail later.

The ink cartridge 43 has a storage element 52 (see FIG. 6), in whichpieces of information, for example, with regard to the remainingquantities of the respective inks, are stored. The storage element 52has an EEPROM. The computer 80 writes and reads the data regarding theremaining quantities of inks into and from the storage element 52 viathe control circuit 60 of the color printer 20. The details of theprocess of reading and writing the data regarding the remainingquantities of inks will be discussed later.

The print head 41 disposed on the lower portion of the carriage 40 hasink ejection heads 44, 45, 46, 47, 48, 49, 50 that respectivelycorrespond to the K, C, LC, M, LM, Y, and DY inks. Ink supply conduits(not shown) are formed for the respective inks in the bottom of thecarriage 40. When the ink cartridges 42 and 43 are attached to thecarriage 40, the respective inks kept in the ink cartridges 42 and 43are supplied to the ink ejection heads 44 through 50 via thecorresponding ink supply conduits. The supply of ink fed to each of theink ejection heads 44 through 50 is ejected from the print head 41 tocreate dots on the printing paper P according to the technique discussedbelow.

FIG. 4A shows the internal structure of the print head 41. Forty eightnozzles Nz are formed in each of the ink ejection heads 44 through 50corresponding to the respective colors. Each nozzle has an ink conduit51 and a piezoelectric element PE arranged on the ink conduit 51. As isknown by those skilled in the art, the piezoelectric element PE deformsits crystal structure by application of a voltage and implements anextremely high-speed conversion of electrical energy into mechanicalenergy. In this embodiment, when a preset voltage is applied betweenelectrodes on either end of the piezoelectric elements PE for apredetermined time period, the piezoelectric element PE is expanded forthe predetermined time period to deform one side wall of the ink conduit51 as shown in FIG. 4B. The volume of the ink conduit 51 is reducedaccording to the expansion of the piezoelectric element PE. A certainquantity of ink corresponding to the reduction is ejected as an inkparticle Ip from the nozzle Nz at a high speed. The ink particle Ipsoaks into the printing paper P set on the platen 36 and creates a doton the printing paper P.

FIGS. 5A and 5B show possible arrangements of ink jet nozzles Nz on theink ejection heads 44 through 50. In the example of FIG. 5A, only theblack (K) ink is kept in the ink cartridge 42, whereas the six differentcolor inks, that is, cyan (C), magenta (M), yellow (Y), light cyan (LC),light magenta (LM), and dark yellow (DY) inks, are kept in the inkcartridge 43. Accommodation of a plurality of different inks in one inkcartridge desirably reduces the required number of ink cartridges andthe total space required for attachment of the ink cartridges. Inanother example as shown in FIG. 5B, the DY ink may be kept with the LCand LM inks in the same ink cartridge. In still other examples, the DYink may be kept with the C, M, and Y inks or with the K ink.

As shown in FIG. 5A, seven nozzle arrays, from which the respectivecolor inks are ejected, are formed in the bottom faces of the respectiveink ejection heads 44 through 50. Each nozzle array includes forty eightnozzles Nz arranged in zigzag at a preset nozzle pitch k. The fortyeight nozzles Nz included in each nozzle array may be arranged inalignment, instead of in zigzag. The zigzag arrangement shown in FIG.5A, however, has an advantage that the nozzle array can be designed tohave a small nozzle pitch k.

Referring to FIG. 5A, the ink ejection heads 44 through 50 of therespective colors are shifted in position in the moving direction of thecarriage 40. Since the nozzles included in each ink ejection head arearranged in zigzag, the nozzles are also shifted in position in themoving direction of the carriage 40. The control circuit 60 of the colorprinter 20 drives the respective ink ejection heads 44 through 50 atsuitable head drive timings by taking into account the positionaldifferences of the nozzles in the course of moving the carriage 40 anddriving the nozzles.

FIG. 6 illustrates the internal structure of the control circuit 60 inthe color printer 20. The control circuit 60 includes a CPU 61, a PROM62, a RAM 63, a PC interface 64 that transmits data to and from thecomputer 80, a peripheral equipment input-output unit (PIO) 65 thattransmits data to and from the sheet feed motor 35, the carriage motor30, and other elements, a timer 66, and a drive buffer 67. The dataregarding the remaining quantities of inks or the quantities ofconsumption of inks are read from or written into the storage element 52incorporated in the ink cartridge 43 via the PIO 65. The drive buffer 67functions to supply dot on/off signals to the ink ejection heads 44through 50. These elements are mutually connected via a bus 68 to allowtransmission of data. The control circuit 60 further includes anoscillator 70 that outputs driving waveforms at selected frequencies anda distributor 69 that distributes the outputs from the oscillator 70 tothe ink ejection heads 44 through 50 at specified timings.

The control circuit 60 constructed as shown in FIG. 6 receives the imagedata FNL output from the computer 80 and temporarily stores the doton/off signals in the RAM 63. The CPU 61 outputs the dot data to thedrive buffer 67 at preset timings synchronously with the operations ofthe sheet feed motor 35 and the carriage motor 30.

The following describes a mechanism of creating dots in response to thedot on/off signals output from the CPU 61 to the drive buffer 67. FIG. 7illustrates connection of one nozzle array in the ink ejection heads 44through 50. The nozzle array in each of the ink ejection heads 44through 50 is included in a circuit, in which the drive buffer 67 worksas the source and the distributor 69 as the sink. The piezoelectricelements PE corresponding to the nozzles Nz included in the nozzle arrayhave one electrodes respectively connected to the respective outputterminals of the drive buffer 67 and the other electrodes collectivelyconnected to the output terminal of the distributor 69. The drivingwaveforms of the oscillator 70 are output from the distributor 69 asshown in FIG. 7. When the CPU 61 outputs the dot on/off signals of therespective nozzles to the drive buffer 67, only the piezoelectricelements PE receiving the ON signal are driven in response to the outputdriving waveforms. The ink particles Ip are thus ejected from thenozzles corresponding to the piezoelectric elements PE that havereceived the ON signal from the drive buffer 67.

The color printer 20 having the hardware configuration discussed abovedrives the carriage motor 30 to move the ink ejection heads 44 through50 of the respective colors relative to the printing paper P in the mainscanning direction, and drives the sheet feed motor 35 to shift theprinting paper P in a sub-scanning direction. Under the control of thecontrol circuit 60, the print head 41 is driven at adequate timingswhile the main scans and sub-scans of the carriage 40 are repeated. Thecolor printer 20 accordingly prints a color image on the printing paperP.

A-2. Structure of Ink Cartridge

FIG. 8A shows the appearance of the ink cartridge 43 attached to thecolor printer 20 of this embodiment. As mentioned previously, the inkcartridge 43 has the total of six different color inks, that is, cyan(C), light cyan (LC), magenta (M), light magenta (LM), yellow (Y), anddark yellow (DY) inks, kept therein. Accommodation of a plurality ofdifferent inks in one ink cartridge desirably reduces the requirednumber of ink cartridges and the total space required for the attachmentof ink cartridges. The ink cartridge 43 has the storage element 52including the EEPROM, in which various pieces of information are storedas discussed later.

The quantities of the respective color inks kept in the ink cartridge 43are determined according to the expected quantities of use of therespective color inks, so as to satisfy the following relations. Thequantity of the DY ink is set greater than the quantity of the Y ink.The quantity of the LC ink is set greater than the quantity of the Cink. The quantity of the LM ink is set greater than the quantity of theM ink. The arrangement of setting the quantities of inks kept in one inkcartridge according to the expected quantities of use of the respectiveinks enables all the color inks to be used up at substantially the sametime. Namely this arrangement reduces the waste of ink.

FIGS. 9A and 9B are graphs showing observed quantities of inkconsumption when natural images, such as landscapes and portraits, areprinted with the color printer 20 of the embodiment. The consumedquantities of the respective color inks are varied to some extent by avariety of settings in the color printer 20 as described later. Theexpected quantities of use of the respective color inks can, however, beroughly specified by such observed values.

FIG. 9A shows the mean consumed quantities of the respective color inkswith regard to typical nine images including landscapes and portraits.In the graphs of FIGS. 9A and 9B, the consumed quantity of each colorink is shown as a relative value to a predetermined reference value.FIG. 9B shows the consumed quantities of the respective color inks whenan N1 sample image is printed out of high definition color digitalstandard image data (ISO/JIS-SCID). The high definition color digitalstandard image data are supplied in the form of CMY image data, so thatthe input image data are converted to RGB image data and output to thecolor printer 20 for printing.

The curves of dotted line in both FIGS. 9A and 9B represent the observedquantities of ink consumption with the color printer that does not usethe DY ink but uses only six inks, C, LC, M, LM, Y, and K. Since thenatural images generally have a large fraction of medium tones, thegreater quantities of the lighter inks, that is, the LC, LM, and Y inks,are used to print the natural images. The DY ink has a color that issimilar to a mixture of the Y, LC, and LM inks as described later. Thesimilar images can thus be printed by creating dots of the DY ink,instead of creating dots of the Y ink, the LC ink, and the LM ink. Thecurves of solid line in both FIGS. 9A and 9B represent the observedquantities of ink consumption when the DY ink as well as the other inksare used to print an image. The ratio of replacement of the Y dots, theLC dots, and the LM dots with the DY dots may be varied according to thecomposition of the DY ink and the usage of the DY dots as discussedlater. The rough tendency is, however, understood from the measurementresults shown in FIGS. 9A and 9B.

As clearly understood from the measurement results of FIGS. 9A and 9B,when a natural image is printed using the DY dots, the consumption ofthe DY ink tends to be greater than that of the Y ink (see the curves ofsolid line in FIGS. 9A and 9B). As mentioned previously, a large numberof the Y dots, the LC dots, and the LM dots are created to print anatural image without using the DY dots (see the curves of dotted linein FIGS. 9A and 9B). The use of the DY ink enables a large portion ofthe Y dots, the LC dots, and the LM dots to be replaceable with the DYdots. In the measurement results of FIGS. 9A and 9B, the consumption ofthe DY ink is approximately double the consumption of the Y ink.

As in the case without the DY dots, in the case with the DY dots, theconsumption of the LC ink tends to be greater than that of the C ink andthe consumption of the LM ink tends to be greater than that of the Mink. Formation of the DY dots enables reduction of the number of the LCdots and the LM dots and thereby ensures a certain margin for therestriction of ink duty. The C dots and the M dots are accordinglyreplaced with the more inconspicuous LC dots and the LM dots. Thisresults in reducing the number of the C dots and the M dots, while notsignificantly varying the total number of the LC dots and the LM dots.In the case with the DY dots, the consumption of the LC ink is thusgreater than the consumption of the C ink, and the consumption of the LMink is greater than the consumption of the M ink.

As shown in FIG. 8, the ink cartridge 43 of the embodiment has a greatercapacity of the DY ink than that of the Y ink, a greater capacity of theLC ink than that of the C ink, and a greater capacity of the LM ink thanthat of the M ink. Namely the quantities of inks kept in the inkcartridge 43 substantially correspond to the observed quantities ofconsumption of the respective color inks shown in FIGS. 9A and 9B. Thiseffectively prevents the waste of inks kept in the ink cartridge.

As described previously, in the color printer 20 of the embodiment, theK ink is kept in the ink cartridge 42, whereas the six color inks otherthan the K ink are kept in the ink cartridge 43. The combination of thecolor inks kept in the ink cartridge is, however, not restricted to thisembodiment, but may be any one of the combinations shown in FIGS. 8Bthrough 8F. In the examples of FIGS. 8B through 8F, the storage element52 is omitted from the illustration. This does not mean that only theink cartridge 43 shown in FIG. 8A has the storage element 52 but theother ink cartridges do not have the storage element 52.

In the case where only the DY ink alone is kept in an ink cartridge asshown in FIG. 8B, there is no necessity of replacing the ink cartridgeuntil the DY ink is completely used up. This arrangement perfectlyprevents any waste of the DY ink. Since the consumption of-the DY ink isgreater than the consumption of the Y ink, it is preferable to set thecapacity of the DY ink greater than the capacity of the Y ink. Thisprevents the frequent replacement of the ink cartridge of the DY ink.The ink cartridge with the only DY ink alone kept therein is attachableto the color printer having a monochromatic ink cartridge, for example,an ink cartridge for black ink. Using a special printer driver for theDY ink available alone or with the ink cartridge of the DY ink enablescreation of the DY dots even in the color printer that has been designedwithout any consideration of the DY ink. Creation of the DY dots enablesan image of high picture quality to be printed, because of the reasonsdiscussed later.

In another example shown in FIG. 8C, the three color inks, DY, LC, andLM inks, are kept in one ink cartridge, whereas the other four colorinks C, M, Y, and K may be kept together in another ink cartridge oronly the K ink alone may be kept in another ink cartridge separatelyfrom still another ink cartridge of the C, M, and Y inks. Thearrangement of keeping the three color inks, DY, LC, and LM inks, whichare used in large quantities to print natural images as shown in FIGS.9A and 9B, together in one ink cartridge separately from the other colorinks preferably prevents the waste of the C, M, and Y inks when only theDY, LC, and LM inks are used up by printing a large number of naturalimages. The arrangement of keeping the K ink alone in one ink cartridgeseparately from the C, M, and Y inks also preferably prevents the wasteof the C, M, and Y inks when only the black ink is used up by printing alarge number of black and white images, such as documents.

As shown in the examples of FIGS. 8D through 8F, the DY ink may be kepttogether with one or a plurality of other inks in one ink cartridge.This arrangement desirably saves the total space required for the inkcartridges.

A special printer driver exclusively designed for the DY ink may beattached to any one the ink cartridges including the DY ink as shown inFIGS. 8A through 8F. For example, when there are a plurality ofdifferent DY inks, the special printer driver attached to the inkcartridge is used corresponding to the DY ink.

As explicitly shown in FIG. 8A, the storage element 52 for storing data,for example, with regard to the quantities of consumption of therespective color inks is mounted on the side face of the ink cartridge43. As described previously with FIG. 6, the color printer 20 can readand write a variety of data from and into the storage element 52. Thefollowing briefly describes the functions of the storage element 52mounted on the ink cartridge 43.

FIG. 10 is an enlarged view illustrating the storage element 52 mountedon the side face of the ink cartridge 43. The storage element 52 has aplurality of connection terminals 53. The ink cartridge 43 is attachedto the carriage 40 of the color printer 20. The inner face of thecarriage 40 that is in direct contact with the ink cartridge 43 has aplurality of connectors (not shown) that are connected with theconnection terminals 53 of the storage element 52. When the inkcartridge 43 is attached to the carriage 40 of the color printer 20, theplurality of connection terminals 53 are electrically connected with theplurality of connectors on the carriage 40 to allow the datatransmission between the color printer 20 and the storage element 52.

FIG. 11 shows the data structure of the EEPROM incorporated in thestorage element 52. The numerals in the left column of FIG. 11 denotethe addresses in the storage element 52 seen from the color printer 20,and the right column of FIG. 11 shows the contents of the informationregistered at the respective addresses. The storage element 52 includesa first storage area 660 and a second storage area 650. The colorprinter 20 enables both the reading and writing operations of data fromand into the first storage area 660, whereas enabling only the readingoperation of data from the second storage area 650. Data on theremaining quantities of the respective color inks are stored in thefirst storage area 660. Other data that are not required updating norfrequently read, for example, the data on the year, month, and date ofmanufacture of the ink cartridge, are stored in the second storage area650. The first storage area 660 is allocated to a region of loweraddresses than those to the second storage area 650. The allocation ofthe first storage area 660, which data are frequently read from andwritten in, to the region of the lower addresses ensures the quick datareading and writing operations by the sequential access. Thisarrangement enables application of an inexpensive EEPROM for theexpendable ink cartridges.

As shown in FIG. 11, the data on the remaining quantities of the C, M,Y, LC, LM, and DY inks are stored in the first storage area 660. Theremaining quantities of the respective color inks are registered in aduplicated manner. The duplicate storage functions as the back-up whenthe data are destroyed, for example, by an accidental power breakdown inthe course of writing data. The remaining quantities of inks are storedwith regard to all the inks kept in the ink cartridge. In the case whereonly the DY ink is kept in the ink cartridge, for example, only theremaining quantity of the DY ink is stored in the first storage area660.

The second storage area 650 stores the data on the time (year and month)of unsealing the ink cartridge, the version data of the ink cartridge,the data on the type of ink, for example, pigments or dyes, the data onthe year, month, and date of manufacture of the ink cartridge, the dataon the production line, the serial number data of the ink cartridge, andthe data showing whether the ink cartridge is new or recycled.

The computer 80 reads the data from the storage element 52 atpredetermined timings, for example, at the time of power supply to thecolor printer 20, and writes the data on the remaining quantities of therespective inks into the storage element 52 at predetermined timings,for example, at the time of completion of the printing operation or atthe time of power cut to the color printer 20. This arrangement enablesthe printer driver 92 to accurately obtain the type of ink currentlyused and the remaining quantity of each ink. The color printer 20 of theembodiment thus enables appropriate printing operations and effectivelyprevents ink from being used up in the course of the printing operation.

A-3. Dark Yellow Ink

FIG. 12 shows an example of ink compositions used in the color printer20 of the embodiment. Each color ink is a mixed solution obtained byadding adequate quantities of each color dye and diethylene glycol forthe adjustment of the viscosity to an aqueous solution of Surfinol. Thedark yellow ink used in this embodiment is prepared by addingsubstantially equivalent quantities of Direct Blue 199, which is the dyeof the cyan ink, and Acid Red 289, which is the dye of the magenta ink,to Direct Yellow 86, which is the dye of the yellow ink. The compositionof the dark yellow ink is, however, not restricted to this example. Thedark yellow ink may contain the varying ratio or quantities of DirectBlue 199 and Acid Red 289 or may be prepared by adding a small quantityof Food Black 2, which is the dye of the black ink, to Direct Yellow 86.The dark yellow ink may also have a less content of Direct Yellow 86 byadding greater quantities of Direct Blue 199 and Acid Red 289 or byadding a greater quantity of Food Black 2. The dye of the yellowcomponent used for the dark yellow ink may be identical with ordifferent from the dye used for the yellow ink. The yellow dyes, such asDirect Yellow 132 and Acid Yellow 23, may be used in place of DirectYellow 86, which is the yellow dye used for the yellow ink.

As clearly understood from the above explanation, the dark yellow inkmay have the following definition based on the ability of reproducingcolors in the color printer. The dark yellow ink has a lower lightnessthan that of the yellow ink. Dots of the dark yellow ink can not expressachromatic gray color alone, but can represent the achromatic color incombination with dots of the cyan ink and dots of the magenta ink. Inthis embodiment, the viscosity of each color ink is adjusted to beapproximately 3 mPa·s. The same control procedure can thus be appliedfor the piezoelectric elements PE allocated to any ink.

FIGS. 14A through 14E are graphs conceptually showing the variations inreflectivity against the wavelength of light with regard to the colorinks used in this embodiment. Referring to FIGS. 14A through 14C, thecyan (C) ink characteristically absorbs light in the wavelength regionof 600 nm to 700 nm, the magenta (M) ink characteristically absorbslight in the wavelength region of 500 nm to 600 nm, and the yellow (Y)ink characteristically absorbs light in the wavelength region of 400 nmto 500 nm.

The graphs of FIGS. 14D and 14E conceptually show the variations inreflectivity against the wavelength of light with regard to differentdark yellow (DY) inks. DY1 ink shown in FIG. 14D corresponds to the DYink having the composition shown in FIG. 12, and DY2 ink shown in FIG.14E corresponds to the DY ink prepared by adding Food Black 2 to DirectYellow 86. Since the DY1 ink contains small quantities of the dyes ofthe cyan ink and the magenta ink in addition to the dye of the yellowink (see FIG. 12), the DY1 ink mainly absorbs the ray of the wavelengthregion characteristic of the yellow ink and also slightly absorbs therays of the wavelength regions characteristic of the cyan ink and themagenta ink. Varying the quantities of addition of Direct Blue 199 andAcid Red 289 changes the absorption the rays of the wavelength regionscharacteristics of the cyan ink and the magenta ink. Since the DY2 inkcontains a small quantity of the dye of the black ink in addition to thedye of the yellow ink, the DY2 ink mainly absorbs the ray of thewavelength region characteristics of the yellow ink and also increasesabsorption over the wavelength region of 500 nm to 700 nm. Varying thequantity of addition of Food Black 2 changes the absorption in thewavelength region of 500 nm to 700 nm. The graphs of FIGS. 14D and 14Eexaggerate the difference in characteristics of light absorption betweenthe DY1 ink and the DY2 ink. The actual difference in characteristics oflight absorption between the DY1 ink and the DY2 ink is not so clear asthat illustrated here.

The comparison between the reflectivity of the DY1 ink or the DY2 inkand the reflectivity of the Y ink shown in FIG. 14C clearly shows thatthe reflectivity of the DY1 ink or the DY2 ink is lowered in thewavelength region of visible rays. This means that both the DY1 ink andthe DY2 ink have lower lightness than that of the Y ink. The change incharacteristics of light absorption with a variation in quantities ofthe dyes added to the dye of the yellow component has certain effects asdiscussed later.

FIG. 13 is a graph showing the curves of lightness with regard to therespective inks having the compositions shown in FIG. 12. The dotrecording ratio plotted as abscissa in the graph of FIG. 13 is an indexrepresenting the percent of dots formed per unit area. For example, thedot recording ratio of 100% represents the state in which dots areformed in all the pixels. The dot recording ratio of 50% represents thestate in which dots are formed in half the pixels. The dot recordingratio of 0% represents the state in which no dots are formed in anypixels. The dot recording ratio is explained in detail later. Thelightness plotted as ordinate in the graph of FIG. 13 represents thebrightness of the image relative to the background color of the printingpaper. The lightness of 100% represents the background color of theprinting paper. The brightness of the image decreases with a decrease inlightness. Any ink has the lightness of 100% at the dot recording ratioof 0%. The lightness decreases with an increase in dot recording ratio,that is, with formation of more dots. Comparison of the brightnessbetween the images at a fixed dot recording ratio shows the differencein lightness between the respective color inks.

The results of the measurement shown in FIG. 13 show that the DY inkhaving the composition shown in FIG. 12 (corresponding to the DY1 inkshown in FIG. 14D) is darker than the Y ink, the LC ink, and the LM inkbut brighter than the C ink, the M ink and the K ink.

The DY ink may have any composition as shown in the examples of FIGS.14D and 14E. FIG. 15 is a graph showing the observed curve ofreflectivity against the wavelength of light with regard to DY inkprepared according to a different principle from those of the DY1 inkand the DY2 ink (hereinafter referred to as the DY3 ink). For thepurpose of reference, the curve of reflectivity with regard to the DY1ink is also plotted by the dotted line. As shown in the graph of FIG.15, like the reflectivity of DY1 ink, the reflectivity of the DY3 inkhas a characteristic area of small reflectivity (that is, the areacharacteristically absorbing light) in the wavelength region of 400 nmto 500 nm. This is characteristic of the yellow ink. The reflectivity ofthe DY3 ink rises in a wavelength region of longer than about 650 nm. Itis known that the sensitivity of human eye to the color is abruptlylowered in the wavelength region of longer than about 650 nm. Althoughthe DY1 ink and the DY3 ink have significantly different behaviors onreflectivity in the wavelength region of longer than 650 nm as shown inFIG. 15, they are recognized as substantially the same color by thevision of the human eye. This means that there is a significant degreeof freedom in setting of the light reflectivity in the wavelength regionof longer than 650 nm. It is not easy to specify the composition of therespective dyes or pigments in the ink for the ideal spectroscopiccharacteristics. The DY ink having the ideal hue is, however, easilyobtained by utilizing the degree of freedom in reflectivity in thewavelength region of longer than 650 nm. As is well known, thesensitivity of human eye to the color is lowered in the wavelengthregion of shorter than 400 nm, as well as in the wavelength region oflonger than 650 nm. The ink can thus be designed by utilizing the degreeof freedom in reflectivity in the short wavelength region.

The following describes, with FIG. 16, the phenomenon that theproperties of the DY ink can be regulated to some extent by utilizingthe degree of freedom in reflectivity in the wavelength region of longerthan 650 nm. FIG. 16 shows the observed colors expressed on the printingpaper under the condition of a gradual increase in recording density ofdots (dot recording ratio) formed with the DY ink on the printing paper.The abscissa represents the a* axis in the L*a*b* colorimetric system,and the ordinate represents the b* axis. The area of positive values (+)along the a* axis substantially corresponds to the red color, whereasthe area of negative values (−) along the a* axis substantiallycorresponds to the green color. The area of positive values (+) alongthe b* axis substantially corresponds to the yellow color, whereas thearea of negative values (−) along the b* axis substantially correspondsto the blue color. The position shown by ST in the graph of FIG. 16shows the coordinates representing the background color of the printingpaper.

In the case where dots are formed with the DY1 ink shown in FIG. 15 onthe printing paper, the color expressed on the printing paper follows alocus shown by the dotted line with an increase in dot recording ratio.Namely the hue becomes slightly greenish with an increase in dotrecording ratio. In the case where dots are formed with the DY2 ink, onthe other hand, the hue does not become greenish with an increase in dotrecording ratio. The minute characteristics of the ink as shown in FIG.16 can be regulated by utilizing the wavelength region of longer than650 nm, where the sensitive of human eye to the color is lowered to givea sufficient degree of freedom in design of the ink. As described laterin detail, the use of the DY ink having the hue becoming greenish withan increase in dot recording ratio significantly improves an imagehaving the hue of green and low lightness. In a similar manner, the useof the DY ink having the hue becoming reddish with an increase in dotrecording ratio significantly improves an image having the hue of redand low lightness. The ink having the hue in a range of 10R to 10GY on aMunsell hue circle is applicable for the DY ink. In the example of theDY3 ink shown in FIG. 15, the reflectivity of light is increased in thewavelength region of longer than 650 nm by utilizing the degree offreedom in design of the ink in this wavelength region. The ink mayalternatively be designed to lower the reflectivity of light in thiswavelength region.

FIG. 17 shows the structure of an ink supplier 55 for feeding a supplyof ink to an ink cartridge. The ink supplier 55 includes a sealed vessel56, in which ink is sealed, a filler inlet 57, through which a supply ofink is fed, and a piston 58 to press the sealed ink out. The dark inkdiscussed above is sealed in the sealed vessel 56 to be not exposed tothe atmosphere. This protects the ink in the ink supplier 55 from achange in properties. When a supply of ink is fed to the ink cartridge,a cap 54 mounted on an end of the filler inlet 57 of the ink supplier 55is removed, and the filler inlet 57 is stuck to an ink supply inlet (notshown) formed in the bottom face of the ink cartridge. The piston 58 isthen pressed down to slowly press the ink out of the sealed vessel 56,so as to feed a supply of ink to the ink cartridge.

B. Image Processing

The color printer 20 forms dots of the respective color inks includingthe DY ink discussed above, so as to print a color image. In order toenable the color printer 20 to create dots of the respective color inks,the computer 80 should carry out predetermined image processing withregard to image data ORG representing a color original image and outputthe processed image data FNL to the color printer 20. The imageprocessing is executed by the printer driver 92 of the computer 80. FIG.18 is a flowchart showing an image processing routine executed by theprinter driver 92.

When the program enters the image processing routine of FIG. 18, the CPU81 in the computer 80 first receives image data to be processed at stepS100. As described previously with FIG. 2, the image data are generatedby the application program 91 and transmitted to the printer driver 92.In the application program 91, the color image data are expressed as acombination of three color images, red (R), green (G), and blue (B). Theimage of each color is expressed as a set of pixels individually havingtone values. In the case of 8-bit image data, each pixel may take one of256 tone values in a range of 0 to 255.

B-1. Process of Converting Resolution

When receiving the image data output from the application program 91,the CPU 81 carries out a process of converting resolution at step S102.As mentioned above, the input image is expressed as a set of pixels. Thelength on a printing medium corresponding to one pixel depends upon thesize of an image to be processed on the printing medium. The number ofdots printable per unit length by the printer (hereinafter referred toas the printer resolution) has been set for each model of the printer.For convenience of the image processing, it is required to make theresolution of the image coincident with the printer resolution. In thecase where the resolution of the image is lower than the printerresolution, linear interpolation is performed to generate a new piece ofimage data between two adjacent pieces of existing data. In the casewhere the resolution of the image is higher than the printer resolution,on the contrary, the resolution is lowered by skipping some pieces ofimage data at a preset rate. The process of step S102 makes theresolution of the image coincident with the printer resolution in thismanner.

B-2. Color Conversion Process

After completion of the resolution conversion process, the CPU 81carries out a color conversion process at step S104. As describedpreviously, the application program 91 expresses a color image as toneimage data of three colors, red (R), green (G), and blue (B). The colorprinter 20, on the other hand, expresses a color image, in principle, bysubtractive mixture of three color stimuli, cyan (C), magenta (M), andyellow (Y). In order to print a color image, it is accordingly requiredto convert the expression of a color image with the three colors R, G,and B to the expression of a color image with the three colors C, M, andY. The process of step S104 carries out such color conversion. Theactual process of this embodiment carries out the color conversion notto the three basic colors C, M, and Y but to the total of seven colorsincluding K, LC, LM, DY. For the clarity of explanation, however, it isassumed that the process carries out the color conversion to the threebasic colors C, M, and Y. The color conversion process changes the toneimage data of R, G, and B respectively having the 256 tone values totone image data of C, M, and Y respectively having the 256 tone values.

In the actual procedure, the CPU 81 refers to a conversion table asshown in FIG. 19, so as to convert the R, G, and B tone values into theC, M, and Y tone values. As shown in FIG. 19, the conversion table is athree-dimensional mathematical table (color solid) having the tonevalues of R, G, and B as axes. In this embodiment, each axis takes thevalues in the range of 0 to 255. A space defined by the mutuallyperpendicular R, G, and B axis is referred to as the color space. Theconversion table divides the color solid into a number of small cubes.Each cube has vertexes, at each of which a corresponding set of the C,M, and Y tone values is registered.

The color conversion is carried out in the following manner by referringto the conversion table. For example, it is assumed that a color definedby RA, GA, and BA as the tone values of R, G, and B is to be expressedby the tone values of C, M, and Y. The process finds a small cube (dV)including a point A having the coordinates (RA,GA,BA) in the colorspace. The process then carries out interpolation with sets of the C, M,and Y tone values registered at the respective vertexes of the cube(dV), so as to calculate the C, M, and Y tone values of the point A.

In this manner, the conversion table allocates a set of the C, M, and Ytone values to each coordinate included in the color solid of R, G, andB tone values. When tone values of the K (black), LC (light cyan), LM(light magenta), and DY (dark yellow) are registered, in addition to thetone values of the C, M, and Y, in the conversion table, a set of the C,M, Y, K, LC, LM, and DY tone values is allocated to each coordinateincluded in the color solid of R, G, and B tone values. In accordancewith another possible application, intermediate sets of C, M, and Y tonevalues, sets of C, M, Y, and K values, or sets of C, M, Y, K, LC, and LMtone values may be stored in the conversion table. The processcalculates the final tone values of C, M, Y, K, LC, LM, and DY from theintermediate values stored in the conversion table.

FIGS. 20A and 20B conceptually show a method of calculating tone valuesof seven colors C, M, Y, K, LC, LM, and DY from the tone values of sixcolors C, M, Y, K, LC, and LM in a shadow area (area having lowlightness). FIG. 20A shows an example in the shadow area of dark red.The tone values of LC and LM are extremely small, while the tone valuesof C, M, and Y are large in the shadow area as shown in FIG. 20A. Thetone value of each color corresponds to the density of dots formed withthe color ink on the printing medium.

FIG. 20B shows a case in which half the tone value of Y is replaced withthe tone value of DY. As explained previously with FIG. 2, the DY inkhas certain contents of the dyes of the cyan ink and the magenta ink.The tone values of C and M are accordingly reduced by the products ofthe DY tone value and the rates of content of the respective dyes. Asshown in FIG. 20B, the reduction results in producing a margin for therestriction of ink duty.

In order to increase the darkness of the dark red from the state shownin FIG. 20A, it is required to decrease the tone values of C, M, and Yand increase the tone value of K (that is, create K dots). As describedpreviously, however, creation of K dots results in the poor granularityunless the K dots are formed in very dark red. When there is a certainmargin for the restriction of ink duty as shown in FIG. 20B, the darkred can be further darkened by increasing the tone value of LC or C.This prevents the poor granularity due to creation of K dots. The marginfor the restriction of ink duty is enhanced by increasing the rate ofreplacement of the Y tone value with the DY tone value or by increasingthe contents of the dyes of the cyan ink and the magenta ink included inthe DY ink, as described later.

In most cases, the color correction process is carried outsimultaneously with the color conversion process. The color correctionprocess corrects the tone values of R, G, and B, in order to eliminatethe effects of different sensitivity characteristics of image scannersthat read color images. Alternatively the color correction processcorrects the tone values of C, M, and Y, in order to eliminate thedifference in color reproduction properties between the printingapparatuses. The color correction enables accurate colors to bereproduced irrespective of the difference between the image scanners orthe printing apparatuses.

B-3. Process of Converting Number of Tones

After the completion of the color conversion process, the CPU 81 carriesout a process of converting the number of tones at step S106. The imagedata after the color conversion represents an image of 256 tones withregard to the seven colors C, M, Y, K, LC, LM, and DY. The printer, onthe other hand, creates dots on the printing paper to reproduce animage, and generally has only two levels, that is, the dot-on state andthe dot-off state. There are variable dot printers and other multi-levelprinters that can print multi-level dots including intermediate states,for example, by varying the size of dots to be created. These printers,however, still have a relatively small number of expressible tones. Itis thus required to convert the image having 256 tones into an imagehaving an extremely small number of tones expressible by the printer.This is the process of converting the number of tones. FIGS. 21A and 21Bshow a process of binarization to convert the number of tones. FIG. 21Ashows image data after the color conversion but before the binarization,and FIG. 21B shows image data after the binarization. The image databefore the binarization have any one of 256 tones in each pixel. Theimage data after the binarization have either one of two values in eachpixel, that is, the dot-on level (the value ‘1’) and the dot-off level(the value ‘0’). In order to show the distribution of dots clearly, inthe image data of FIG. 21B, pixels having the value ‘1’ are hatched andpixels having the value ‘0’ are open.

The structure of this embodiment determines the dot on-off conditionswith regard to the seven colors C, M, Y, K, LC, LM, and DY. There are avariety of methods applicable for the determination, all of whichnaturally have some advantages and disadvantages. The color printer 20of the embodiment causes the user to select an appropriate method forthe determination. There are typically two methods, the error diffusionmethod and the systematic dither method. The error diffusion methodensures the high picture quality, whereas the systematic dither methodenables the high-speed processing. The following briefly describes theoutlines of the error diffusion method and the systematic dither method.

B-4. Binarization by Error Diffusion Method

FIG. 22 is a flowchart showing a binarization process by the errordiffusion method. The technique of the embodiment carries out thebinarization process individually with regard to the respective colorsC, M, Y, K, LC, LM, and DY after the color conversion. The followingdescription does not specify the color, for the clarity of explanation.When the program enters the binarization process, the CPU 81 reads imagedata Cd at step S200. The image data Cd have 256 tones with regard toeach color after the color conversion. The CPU 81 generates correctiondata Cdx from the input image data Cd at step S202. The error diffusionmethod distributes an error of binarization generated with regard toeach processed pixel to a plurality of unprocessed pixels in thevicinity of the processed pixel with certain weights. The process ofstep S202 adds a sum of error portions distributed from the surroundingprocessed pixels to a pixel of interest, which is currently beingprocessed, to calculate the correction data Cdx. FIG. 23 shows theweights added to the surrounding pixels, to which an error of a pixel ofinterest PP is distributed. The error of binarization generated in thepixel of interest PP is distributed to several adjoining pixels in thescanning direction of the carriage, as well as to several adjoiningpixels in the feeding direction of the printing paper P withpredetermined weights, ¼, ⅛, and {fraction (1/16)}. The error diffusionprocess is described later more in detail. The correction data Cdx thusgenerated is compared with a predetermined threshold value th set foreach color at step S204. In the case where the correction data Cdx isnot smaller than the threshold value th, a value ‘1’ representingcreation of a dot is set to a resulting value Cdr showing the result ofthe binarization at step S206. In the case where the correction data Cdxis smaller than the threshold value th, on the other hand, a value ‘0’representing creation of no dot is set to the resulting value Cdr atstep S208. The predetermined threshold value th is a reference valueused to determine whether or not a dot is to be created in each pixel.

The CPU 81 then calculates an error of binarization in the pixel ofinterest and diffuses the calculated error to the peripheral pixels inthe vicinity of the pixel of interest at step S210. The error is equalto a difference by subtracting the result of the tone number conversionfrom the tone value of the original image data. For example, it isassumed that there is a pixel having the tone value ‘64’ in the originalimage data. When a dot is created in the pixel, the converted resultcorresponding to a tone value ‘255’ is expressed in the pixel. In thiscase, there is an error of 64−256=−191. When no dot is created in thepixel, on the contrary, there is an error of 64−0=64.

The error thus calculated is diffused into the peripheral pixels withthe certain weights shown in FIG. 23. For example, when the target ofpixel PP has the calculated error corresponding to the tone value ‘64’,an error portion corresponding to a tone value ‘16’, which is ¼ of theerror, is diffused to an adjoining pixel P1. The total of such diffusederrors is reflected on the image data Cd, so as to generate thecorrection data Cdx at step S202 described above. The series of theprocessing is repeated with regard to all the pixels at step S212. Theimage data representing the dot on-off conditions as shown in FIG. 21Bare eventually obtained.

The method of performing the color conversion to generate the tone imagedata of seven colors C, M, Y, K, LC, LM, and DY and carrying out thebinarization individually for the respective colors simplifies thecontents of the processing with regard to each color and thus enablesthe quick processing. The independent and simplified processing withregard to each color enables parallel data conversion using an exclusiveimage processing apparatus. This arrangement ensures the quickbinarization even by the error diffusion method.

In the case of the binarization by the error diffusion method, anotherpossible procedure applicable to the color conversion process (step S104in the flowchart of FIG. 18) generates image data of the four basiccolors C, M, Y, and K, and determines the dot on-off conditions of the Cand LC dots based on the tone data of C, the dot on-off conditions ofthe M and LM dots based on the tone data of M, and the dot on-offconditions of Y and DY dots based on the tone data of Y. This methodsimplifies and speeds up the color conversion process.

B-5. Binarization by Systematic Dither Method

The principle of binarization by the systematic dither method isdescribed with FIG. 24. In this example, it is assumed that the imagedata Cd may take the value in the range of 0 to 255, and a dither matrixhas values in the range of 0 to 254. For simplicity of explanation, theexample of FIG. 24 shows only part of the image data corresponding to4×4 pixels. As shown in FIG. 24, the tone values of the image data Cd inthe respective pixels are compared with the corresponding thresholdvalues included in the dither matrix. In the case where the value of theimage data Cd is greater than the corresponding threshold value in thedither matrix, the dot is to be created. In the case where the value ofthe image data Cd is not greater than the corresponding threshold value,on the other hand, the dot is not to be created. The pixels hatched inFIG. 24 represent pixels in which the dot is to be created.

As described above, the binarization by the systematic dither methodcompares the tone values of the image data in the respective pixels withthe corresponding threshold values included in the dither matrix, anddetermines the dot on-off conditions in all the pixels with regard tothe seven colors C, M, Y, K, LC, LM, and DY based on the results of thecomparison.

Like in the case of the binarization by the error diffusion methoddescribed previously, in the case of the binarization by the systematicdither method, another possible procedure applicable to the colorconversion process (step S104 in the flowchart of FIG. 18) generatesimage data of the four basic colors C, M, Y, and K, and determines thedot on-off conditions of the C and LC dots based on the tone data of C,the dot on-off conditions of the M and LM dots based on the tone data ofM, and the dot on-off conditions of Y and DY dots based on the tone dataof Y. The color conversion process of this procedure requires the imagedata generated only with regard to the four colors. This arrangementsimplifies the color conversion process. This arrangement also preventsdots of the same color system, for example, a C dot and an LC dot, frombeing formed in an overlapping manner in one pixel, thereby improvingthe picture quality.

B-6. Interlace Process

Referring back to the flowchart of FIG. 18, after the completion of theprocess of converting the number of tones, the CPU 81 starts aninterlace process at step S108. The interlace process reorders the imagedata, which have been converted to the dot on-off conditions by theprocess of converting the number of tones, in a sequent to betransferred to the color printer 20. As discussed above, the colorprinter 20 drives the print head 41 to form rows of dots (raster lines)on the printing paper P while repeating the main scan and the sub-scanof the carriage 40. As described previously with FIG. 4, each of the inkejection heads 44 through 50 has the plurality of nozzles Nz, so that aplurality of raster lines are formed by each pass of the main scan. Eachpair of adjoining raster lines formed by the same pass are apart fromeach other by the nozzle pitch k. Raster lines aligned at the intervalsof each pixel are formed according to the following control procedure.The control procedure first forms a plurality of raster lines at theintervals of the nozzle pitch k, slightly shifts the position of eachink ejection head, and forms new raster lines between the existingraster lines. In order to improve the picture quality of the resultingprinted image, the control procedure may cause each raster line to beformed by plural passes of the main scan. In order to shorten theprinting time, the control procedure may cause dots to be formed by bothforward passes and backward passes of the main scan.

After completion of the interlace process, the image data are output asthe printable image data FNL to the color printer 20 at step S110.

C. Results of Simulations

In order to confirm the effects of the DY ink on the improvement inpicture quality, the simulative computation discussed below was carriedout. The following conditions were set for the simulative computation:

Condition 1: The color ‘red’ is expressed by forming both M dots and Ydots at a dot recording ratio of 100%;

Condition 2: The color ‘black’ is expressed by forming K dots at a dotrecording ratio of 100%;

Condition 3: K dots are equivalently replaceable with a combination of CDots, M dots, and Y dots at the same density as that of the K dots;

Condition 4: LC dots are equivalently replaceable with C dots at a ¼ dotrecording ratio;

Condition 5: LM dots are equivalently replaceable with M dots at a ¼ dotrecording ratio; and

Condition 6: DY dots are equivalently replaceable with a combination ofLC dots, LM dots, and Y dots at the same density as that of the DY dots.

The actual printing operation is performed under more complicatedconditions. For example, the rate of replacement of each ink (that is,the rate of each color ink that does not change the output color byreplacement) varies in a very complicated manner according to the actualprinting conditions, and rarely gives a fixed value as shown by theabove conditions. The results of the simulations discussed below do notstrictly represent the actual printing results. The qualitative effectsof the DY ink on the improvement in picture quality by the simulativecomputation are, however, sufficiently applicable to the actual printingresults.

C-1. Gradation Pattern from Red to Black

FIGS. 25A, 25B, and 25C show results of simulative computation of thedot recording ratio with regard to each color ink in the case ofprinting a gradation pattern gradually becoming dark from red to blackwith the color printer 20 of the embodiment. According to the aboveconditions, the gradation pattern from red to black is a pattern havingthe linearly increasing dot recording ratio of C dots from 0% to 100%while keeping a dot recording ratio of 100% with regard to both the Mdots and the Y dots.

On the abscissa of each graph, the value of 0% represents the pure color‘red’ and the value of 100% represents the pure color ‘black’. The color‘red’ expressed on the printing paper is gradually darkened with anincrease in value on the abscissa. FIG. 25A shows the results of thesimulation with the dots of the DY ink in the case of using a sheet ofprinting paper having a restriction of ink duty equal to 220%.

As shown in FIG. 25A, at the value of 0% on the abscissa (the pure color‘red’), only the M dots and the Y dots are formed at the dot recordingratio of 100% on the printing paper. The lightness of the color islowered (that is, darkened) with an increase in dot recording ratio ofthe LC dots while keeping the dot recording ratios of both the M dotsand the Y dots at 100%. When the dot recording ratio of the LC dotsreaches 20% (approximately 5% on the abscissa), the total recordingratio of the Y, M, and LC dots becomes equal to 220%. The restriction ofink duty set for the printing paper does not allow creation of dots atthe greater density. Formation of the DY dots is thus commenced at thevalue of about 5% on the abscissa, while the dot recording ratio of theY dots is gradually decreased. The DY dots formed in the hue of red arenot so conspicuous, because of the following reason. According to theabove condition 6, formation of the DY dots is equivalent to formationof the Y dots, the LM dots, and the LC dots at the same quantity as thatof the DY dots. The Y dots or the LM dots formed in an image where boththe Y dots and M dots have been formed at the dot recording ratio of100% are inconspicuous against the background. The conspicuousness ofthe DY dots formed in the hue of red is as low as that of the LC dots,and the DY dots are thus significantly inconspicuous.

It can be assumed that the DY ink includes the LC ink and the LM ink inaddition to the Y ink (condition 6 given above). Formation of the DYdots accordingly decreases the dot recording ratios of both the LC dotsand the M dots. The decrease in dot recording ratios of the LC dots andthe M dots gives a certain margin for the restriction of ink duty, andthus allows a further increase in dot recording ratio of the LC dots.After the sum of the dot recording ratios of the M, Y, and LC dotsreaches the restriction of ink duty, the replacement of the Y dots withthe DY dots enables the lightness of the color ‘red’ expressed on theprinting paper to be lowered (that is, the value on the abscissa to beincreased). In this stage, no use of the conspicuous C dots desirablyprevents the granularity from being worsened.

After the perfect replacement of all the Y dots with the DY dots, nofurther increase in formation of the DY dots is allowed. The value onthe abscissa is accordingly increased by gradually replacing the LC dotswith the C dots having the higher density. Formation of the C dots iscommenced at the value of about 40% on the abscissa as shown in thegraph of FIG. 25A. The C dots have a relatively low lightness and arerather conspicuous in the color of bright red to worsen the granularity.As in the case of FIG. 25A, however, the C dots are not so conspicuousin the color of dark red, which is expressed by the value of bout 40% onthe abscissa, thereby not worsening the granularity.

When the sum of the dot recording ratios of the C, M, and DY dotsreaches the restriction of ink duty, no further increase in formation ofdots is allowed. The dot recording ratios of the respective C, M, and DYdots are thus decreased, while formation of the K dots is commenced. Asdescribed previously, the K dots have an extremely low lightness (thatis, the K dots are very dark) and are rather conspicuous tosignificantly worsen the granularity, unless they are formed in thesufficiently dark background. As shown in FIG. 25A, however, formationof the K dots is commenced at the value of about 70% on the abscissa.The color ‘red’ expressed on the printing paper thus already has asignificantly low lightness, so that the K dots are not conspicuous tolower the picture quality. At the final stage, only the K dots areformed at the dot recording ratio of 100%. The gradation pattern printedon the printing paper thus naturally and gradually changes the colorfrom red, where only the M dots and the Y dots are formed at therecording ratio of 100%, to black, where only the K dots are formed atthe recording ratio of 100%. Formation of the C dots is commenced at thevalue of about 40% on the abscissa, and formation of the K dots iscommenced at the value of about 70% on the abscissa. These dots areaccordingly not conspicuous to lower the picture quality.

FIG. 25B shows the results of the simulative computation of the dotrecording ratio with regard to each color ink in the case of printing agradation pattern from red to black without the DY dots on the sheet ofprinting paper having the restriction of ink duty equal to 220%. Thepure color ‘red’ (the value of 0% on the abscissa) is gradually darkenedwith an increase in dot recording ratio of the LC dots. Due to therestriction of ink duty, formation of the C dots should be commencedwhen the dot recording ratio of the LC dots reaches 20%. In this case,formation of the C dots is required at the value of about 5% on theabscissa, where the color of still bright red is expressed on theprinting paper. While the LC dots formed in the color of bright red arenot so conspicuous, the C dots, which have a higher density than that ofthe LC dots, formed in the color of bright red as in the case of FIG.25B are rather conspicuous and worsen the granularity.

After the perfect replacement of all the LC dots with the C dots, nofurther increase in formation of dots is allowed due to the restrictionof ink duty. Formation of the K dots is accordingly commenced, while thedot recording ratios of the M dots and the Y dots are graduallydecreased. This state is at the value of about 25% on the abscissa inthe graph of FIG. 25B. Since the K dots have an extremely low lightness(that is, the K dots are very dark), formation of the K dots at thevalue of about 25% on the abscissa significantly worsens thegranularity.

As described above, when the gradation pattern from red to black isprinted without using the DY ink on the printing paper having therestriction of ink duty equal to 220%, the C dots are conspicuous in thecolor of still bright red and the K dots are conspicuous in the color ofrelatively dark red. This gives an image of the poor granularity. Inother words, the use of the DY ink improves the granularity. If the DYdots themselves are rather conspicuous, the use of the DY ink ismeaningless even though the DY ink prevents the granularity from beingworsened due to the C dots or the K dots. The components of the Y inkand the LM ink included in the DY ink are not conspicuous against thebackground ‘red’ color. This means that only the component of the LC inkincluded in the DY ink has a possibility of conspicuousness. Theconspicuousness of the DY dots formed in the red background is thussubstantially equivalent to that of the LC dots. The use of the DY inkaccordingly gives an image of extremely favorable granularity withoutany significant conspicuousness of dots.

FIG. 25C shows the results of the simulative computation of the dotrecording ratio with regard to each color ink in the case of printing agradation pattern from red to black without the DY dots on another sheetof printing paper having a restriction of ink duty equal to 260%. Thepure color ‘red’ (the value of 0% on the abscissa) is gradually darkenedwith an increase in dot recording ratio of the LC dots. Due to therestriction of ink duty, replacement of the LC dots with the C dotsshould be commenced to further darken the color of red when the dotrecording ratio of the LC dots reaches 60% (the value of 15% on theabscissa). When the dot recording ratio of the C dots reaches 60% (thevalue of 65% on the abscissa), no further formation of the C dots isallowed. Formation of the K dots is thus commenced, while the dotrecording ratios of the C, M, and Y dots are gradually decreased. At thefinal stage, only the K dots are formed at the dot recording ratio of100% (pure ‘black’ color). According to the comparison between thegraphs of FIGS. 25A and 25C, both the timing of commencing the formationof the C dots and the timing of commencing the formation of the K dotsare earlier in the case of FIG. 25C than in the case of FIG. 25A. Namelythe dots are more conspicuous to worsen the granularity in the case ofFIG. 25C, compared with the case of FIG. 25A. Based on the simulationconditions given previously, the improvement in picture quality by usingthe DY ink is greater than the improvement in picture quality bychanging the printing paper having the restriction of ink duty equal to220% to the printing paper having the restriction of ink duty equal to260%.

The above results of the simulations suggest the usage of the DY ink. Inthe case of printing a gradation pattern from red to black, theformation of dots with the DY ink starts prior to the formation of dotswith the C ink. The DY ink has a hue closest to that of the Y ink amongthe three basic color inks, C, M, and Y. The dots of the M ink and thedots of the Y ink have been created in advance to express the hue ofred. The formation of dots with the DY ink is thus not commenced earlierthan the formation of dots with the M ink and the Y ink.

There is another suggestion with regard to the usage of the DY ink. Inthe case of printing a gradation pattern from red to black, formation ofthe dots with the DY ink starts after the formation of dots with the LCink. The DY ink has a hue closest to that of the Y ink among the threebasic color inks, C, M, and Y. It can thus be thought that the dots ofthe DY ink are created together with the dots of the LC ink.

In the prior art color printer using the six color inks, C, M, Y, K, LC,and LM, the quantities of consumption of the Y, LC, and LM inks aregreater than the quantities of consumption of the C and M inks. Asdescribed previously, the C, M, Y, LC, and LM inks are often kept in oneink cartridge 43. According to images to be printed, the Y, LC, and Minks are used up to require a replacement of the ink cartridge 43 thatstill has the remains of the C and M inks. The color printer 20 of theembodiment uses the DY ink in place of the Y ink in some occasions andthereby decreases the quantity of consumption of the Y ink. Since the DYink contains the dyes of cyan and magenta, the use of the DY ink alsodecreases the quantities of consumption of the LC ink and the LM ink.The use of the DY ink thus enables all the other color inks to beconsumed in a relatively equal manner and desirably reduces thefrequency of replacement of the ink cartridge. The DY ink may be kepttogether with the LC ink and the LM ink in the same ink cartridge. Thisenables replacement of only the ink cartridge including the LC, LM, andDY inks having the greater quantities of consumption.

The above description regards the gradation pattern from red to black.The gradation pattern from red to black is only an example of gradationpatterns starting from the condition that dots of only two color inks(in this example, the Y dots and the M dots) have already been formed.Similar effects are thus naturally exerted in the case of printing agradation pattern from green to black with replacement of the M dotswith the C dots and the LM dots with the LC dots. The effects of varyingthe quantities of the cyan dye and the magenta dye added to the DY inkwill be described later.

C-2. Gradation Pattern from Magenta to Black

FIGS. 26A, 26B, and 26C show results of simulative computation of thedot recording ratio with regard to each color ink in the case ofprinting a gradation pattern from magenta to black with the colorprinter 20 of the embodiment. The conditions set for the simulativecomputation are identical with the conditions used for the simulation ofthe gradation pattern from red to black. FIG. 26A shows the results ofthe simulative computation with the DY dots in the case of the printingpaper having the restriction of ink duty equal to 220%. FIG. 26B showsthe results of the simulative computation without the DY dots in thecase of the printing paper having the restriction of ink duty equal to220%. FIG. 26C shows the results of the simulative computation withoutthe DY dots in the case of the printing paper having the restriction ofink duty equal to 260%.

As shown in FIG. 26A, in the gradation pattern from magenta to black,the dot recording ratios of the LC dots and the Y dots are graduallyincreased from the initial state (the value of 0% on the abscissa) inwhich the M dots have a dot recording ratio of 100%. According to thecondition 4 mentioned previously, the dots of the LC ink are equivalentto ¼ dots of the C ink. The rate of increase in dot recording ratio ofthe LC dots is thus four times the rate of increase in dot recordingratio of the Y dots. When the dot recording ratios of the LC dots andthe Y dots increase and the sum of the dot recording ratios of the Mdots, the Y dots, and the LC dots reach the restriction of ink duty,replacement of the Y dots with the DY dots is commenced. After theperfect replacement of all the Y dots with the DY dots, replacement ofthe LC dots with the C dots is commenced. According to the results ofthe simulation shown in FIG. 26A, the formation of the C dots starts atthe value of about 35% on the abscissa. As described previously, the DYink contains the components of the LM ink and the LC ink, formation ofthe DY dots is equivalent to formation of the same number of the LM dotsand the LC dots (see the condition 6 mentioned above). The increase indot recording ratio of the DY dots accordingly decreases the dotrecording ratio of the M dots and reduces the rate of increase information of the C dots.

When the sum of the dot recording ratios of the C, M, and DY dotsreaches the restriction of ink duty, formation of the K dots iscommenced. According to the results of the simulation shown in FIG. 26A,the formation of the K dots starts at the value of about 80% on theabscissa. The increase in dot recording ratio of the K dots decreasesthe dot recording ratios of the C, M, and DY dots. At the final stage,only the K dots are formed at the dot recording ratio of 100% (pure‘black’ color). The resulting printed image on the printing paper is agradation pattern having the hues gently changing from magenta to black.

While FIG. 26A shows the results of the simulation with the DY dots,FIG. 26B shows the results of the simulative computation of the dotrecording ratio with regard to each color ink in the case of printing agradation pattern from magenta to black without the DY dots on theprinting paper having the restriction of ink duty equal to 220%.Compared with the case with the DY dots shown in FIG. 26A, in the casewithout the DY dots shown in FIG. 26B, the formation of the C dots iscommenced at the slightly earlier timing and the formation of the K dotsis commenced at the significantly earlier timing. Starting the formationof the K dots at the value of about 60% on the abscissa like the resultsof the simulation shown in FIG. 26B drastically worsens the granularityof the resulting printed image. In other words, the use of the DY dotssignificantly improves the granularity of the resulting printed image.The improvement in granularity is attained by the fact that the DY inkcontains the cyan dye and the magenta dye. Formation of the DY dots isequivalent to formation of certain quantities of the C dots and the Mdots that correspond to the contents of the dyes. Replacement of the Ydots with the DY dots in a shadow area (for example, in the area havingthe value of about 75% on the abscissa) decreases the dot recordingratios of the M dots and the C dots. This ensures a certain margin forthe restriction of ink duty and thereby delays the timing of startingthe formation of the K dots.

As described above, the use of the DY dots significantly delays thetiming of starting the formation of the K dots and slightly delays thetiming of starting the formation of the C dots. This results in asignificant improvement in granularity. If the DY dots that startformation at a relatively early timing are conspicuous, the granularityof the resulting printed image is not actually improved. Theconspicuousness of the DY dots is thus a key factor. As describedpreviously, the DY ink includes the components of the LM ink, the LCink, and the Y ink (see the condition 6 mentioned above). When the dotsof the DY ink are formed in the magenta background, the component of theLM ink included in the DY ink is inconspicuous against the background.The dots of the other ink components, that is, the LC dots and the Ydots, are not so conspicuous in the magenta background. Formation of theDY dots is substantially equivalent to formation of the LC dots and theY dots in an overlapping manner. The dots of both the LC ink and the Yink are not so conspicuous as the dots of the C ink and the K ink.Formation of the DY dots in the magenta background even at a relativelyearly timing thus does not significantly worsen the granularity. In thecase of printing a gradation pattern from magenta to black, the use ofthe DY dots desirably delays the timings of starting the formation ofthe C dots and the K dots and thus significantly improves thegranularity of the resulting printed image.

FIG. 26C shows the results of the simulative computation of the dotrecording ratio with regard to each color ink in the case of printing agradation pattern from magenta to black without the DY dots on theprinting paper having the restriction of ink duty equal to 260%. Theresults of the simulative computation shown in FIG. 26C are comparedwith those shown in FIG. 26A. The timings of starting the formation ofthe C dots and the K dots in the case of FIG. 26C are almost the same asthose in the case of FIG. 26A. When a gradation pattern from magenta toblack is printed, substantially similar effects of improvement inpicture quality are attained in the case of printing with the DY dots onthe printing paper having the restriction of ink duty equal to 220% andin the case of printing without the DY dots on the printing paper havingthe restriction of ink duty equal to 260%.

As shown in the results of the simulations in FIGS. 26A, 26B, and 26C,in the case of printing a gradation pattern from magenta to black, theuse of the DY dots effectively prevents the granularity from beingworsened and thereby improves the picture quality of the resultingprinted image. Another effect of using the DY ink is reducing thequantities of consumption of the Y ink, the LC ink, and the LM ink.

The above results of the simulations suggest the usage of the DY ink. Inthe case of printing a gradation pattern from magenta to black, theformation of dots with the DY ink starts prior to the formation of dotswith the C ink and after the formation of dots with the Y ink. The DYink has a hue closest to that of the Y ink among the three basic colorinks, C, M, and Y. The dots of the M ink have been created in advance toexpress the hue of magenta.

There is another suggestion with regard to the usage of the DY ink. Inthe case of printing a gradation pattern from magenta to black,formation of the dots with the DY ink starts after the formation of dotswith the LC ink. The DY ink has a hue closest to that of the Y ink amongthe three basic color inks, C, M, and Y. It can thus be thought that thedots of the DY ink are created together with the dots of the LC ink.

The above description regards the gradation pattern from magenta toblack as an example of gradation patterns starting from the conditionthat dots of only one color ink have already been formed. Similareffects are thus naturally exerted in the case of printing a gradationpattern from cyan or yellow to black with replacement of the M dots withthe C dots or the Y dots.

C-3. Gradation Pattern from White to Black

FIGS. 27A, 27B, and 27C show results of simulative computation of thedot recording ratio with regard to each color ink in the case ofprinting a gradation pattern from white to black with the color printer20 of the embodiment. The conditions set for the simulative computationare identical with the conditions used for the simulation of thegradation pattern from red to black. FIG. 27A shows the results of thesimulative computation with the DY dots in the case of the printingpaper having the restriction of ink duty equal to 220%. FIG. 27B showsthe results of the simulative computation without the DY dots in thecase of the printing paper having the restriction of ink duty equal to220%. FIG. 27C shows the results of the simulative computation withoutthe DY dots in the case of the printing paper having the restriction ofink duty equal to 260%.

As shown in FIG. 27A, in the case of printing a gradation pattern fromwhite to black, formation of the LC dots, the LM dots, and the Y dotsgradually increases from the initial state in which no dots have beenformed. When the dot recording ratios of the LC dots and the LM dotsapproach to 100%, replacement of the LC dots and the LM dotsrespectively with the C dots and the M dots is commenced. The DY inkcontains the components of the LC ink and the LM ink (see the condition6 given previously). Replacement of the Y dots with the DY dots beforethe dot recording ratios of the LC dots and the LM dots reach 100% thuseffectively delays the timings of starting the formation of the C dotsand the M dots. The delay of the timings of starting the formation ofthe C dots and the M dots desirably makes the dots more inconspicuousand thereby prevents the granularity from being worsened in theresulting printed image.

With an increase in dot recording ratios of the C, M, and DY dots, thelightness of the color expressed on the printing paper is graduallylowered to darker gray. When the sum of the dot recording ratios of theC, M, and DY inks reaches the restriction of ink duty, formation of theK dots is commenced and the dot recording ratios of the C, M, and DYdots are gradually decreased. At the final stage, only the K dots areformed at a dot recording ratio of 100%. The resulting printed image onthe printing medium is a gradation pattern having the color gentlychanging from white to black.

The results of the simulation in the case with the DY dots shown in FIG.27A are compared with the results of the simulation in the case withoutthe DY dots shown in FIG. 27B. The formation of the DY dots desirablydelays the timing of starting the formation of the K dots. According tothe condition 6 mentioned previously, the DY ink contains the componentsof the LC ink, the LM ink, and the Y ink. Replacement of the Y dots withthe DY dots thus reduces the formation of the C dots and the M dots.This gives a certain margin for the restriction of ink duty and therebydelays the timing of starting the formation of K dots.

In the case of printing a gradation pattern from white to black, the useof the DY dots desirably delays the timings of starting formation of theC dots and the M dots and starting formation of the K dots, therebypreventing the granularity from being worsened and improving the picturequality of the resulting printed image.

FIG. 27C shows the results of the simulative computation without the DYdots in the case of the printing paper having the restriction of inkduty equal to 260%. As clearly understood from the comparison betweenthe results of FIG. 27C and the results of FIG. 27A, the C dots and theK dots start formation at substantially the same timings. In the case ofprinting a gradation pattern from white to black, the improvement inpicture quality by the use of the DY dots is thus substantiallyidentical with the improvement in picture quality by changing therestriction of ink duty set for the printing paper from 220% to 260%.

The above results of the simulations suggest the usage of the DY ink. Inthe case of printing a gradation pattern from white to black, theformation of dots with the DY ink starts prior to the formation of dotswith the C ink and the M ink. The DY ink has a hue closest to that ofthe Y ink among the three basic color inks, C, M, and Y. The formationof dots with the DY ink starts after the formation of dots with the Yink. The dots of the DY ink are more conspicuous than the dots of the Yink. Formation of the dots of the DY ink in an overlapping manner on thedots of the Y ink gives a printed image of high picture quality withless conspicuousness of dots. The dots of the DY ink may, however, beformed in place of the dots of the Y ink or simultaneously with the dotsof the Y ink. The dots of the DY ink are not so conspicuous as the dotsof the C ink or the M ink. It is thus not necessary to create the DYdots in an overlapping manner on the Y dots. Any of these arrangementsdoes not cause the DY dots to be made conspicuous and lower the picturequality of the resulting printed image. The use of the DY ink desirablyreduces the total quantity of ink consumption.

There is another suggestion with regard to the usage of the DY ink. Inthe case of printing a gradation pattern from white to black, formationof the dots with the DY ink starts after or simultaneously with theformation of dots with the LC ink and the LM ink. The DY ink has a hueclosest to that of the Y ink among the three basic color inks, C, M, andY. It can thus be thought that the dots of the DY ink are createdtogether with the dots of the LC ink and the dots of the LM ink.

The simulations discussed above aim at preventing the deterioration ofthe granularity and improving the picture quality of the resultingprinted image. When there is a margin for the restriction of ink duty,the dots of the ink having less conspicuousness are thus selectivelycreated. As long as there is no problem in granularity, however, thereplacement of the LC dots with the C dots, the LM dots with the M dots,and the Y dots with the DY dots may be commenced at the earlier timingsthan those discussed in the simulations. This makes the points ofstarting formation of the C dots, the M dots, the DY dots, and the Kdots closer to the value of 0% on the abscissa. According to thecondition 6 given above, it is possible to replace the same quantitiesof the Y dots, the LC dots, and the LM dots with the DY dots. Thereplacement with the DY dots at the earlier timing thus favorablyreduces the total quantity of ink consumption.

The use of the DY ink gives an image of better granularity under thecondition of a fixed quantity of total ink consumption or prints animage of equivalent picture quality with a less quantity of total inkconsumption. The appropriate setting can thus be selected for the use ofthe DY ink based on the priority to the picture quality, the priority tothe less quantity of total ink consumption, or the compatibility ofthese two effects.

As described above, the use of the DY ink improves the granularity,which may be worsened by the conspicuousness of the cyan dots, themagenta dots, or the black dots in a gradation pattern to the shadowarea.

Dark cyan ink and dark magenta ink may also be used for the dark ink.Like the dark yellow ink, these dark inks have the effects of improvingthe granularity based on the margin for the restriction of ink duty andsaving the total quantity of ink consumption. The use of the dark cyanink improves the granularity, which is worsened by the yellow dots andthe magenta dots. Similarly the use of the dark magenta ink improves thegranularity, which is worsened by the yellow dots and the cyan dots. Theyellow dots having a high lightness are, however, originallyinconspicuous and are not the main factor of the worsened granularity.The use of the dark cyan ink thus improves the worsened granularitymainly due to the magenta dots. Similarly the use of the dark magentaink improves the worsened granularity mainly due to the cyan dots. Theuse of the dark yellow ink, on the other hand, improves the worsenedgranularity due to both the cyan dots and the magenta dots, and is thusmost effective. The dark yellow ink having the yellow dye as the maincomponent is less inconspicuous than the dark cyan ink or the darkmagenta ink. From the viewpoint of the improved granularity, the use ofthe dark yellow ink is most desirable.

C-4. Application to Printer with Four Color Inks

The above description regards the effects of the use of the DY ink inthe color printer using the six color inks C, M, Y, K, LC, and LM. Theuse of the DY ink, however, exerts the similar effects in the colorprinter using only the four color inks C, M, Y, and K and the colorprinter using only the three color inks C, M and Y.

FIGS. 28A, 28B, and 28C show results of simulations for confirming theeffects of the use of the DY ink in the case of printing a gradationpattern from red to black with the color printer using only the fourcolor inks C, M, Y, and K. FIG. 28A shows the results of simulativecomputation of the dot recording ratio with regard to each color ink inthe case of printing with the DY dots on the printing paper having therestriction of ink duty equal to 220%. FIG. 28B shows the results ofsimulative computation of the dot recording ratio with regard to eachcolor ink in the case of printing without the DY dots on the printingpaper having the restriction of ink duty equal to 220%. FIG. 28C showsthe results of simulative computation of the dot recording ratio withregard to each color ink in the case of printing without the DY dots onthe printing paper having the restriction of ink duty equal to 260%.

The following effects are expected from the results of the simulativecomputation shown in FIG. 28A. In the color printer using only the fourcolor inks, since the LC ink is not used, it is required to startformation of the C dots at an early timing. As discussed previously, theC dots formed in the color of bright red are rather conspicuous andsignificantly worsen the granularity. In the case with the use of the DYink as shown in FIG. 28A, the color of red is gradually darkened byreplacing the Y dots with the DY dots. The conspicuousness of the DYdots formed in the red background is as low as that of the LC dots. Thereplacement of the Y dots with the DY dots thus does not worsen thegranularity.

After the perfect replacement of all the Y dots with the DY dots, it isrequired to create the C dots. The formation of the DY dots has alreadylowered the lightness of the color ‘red’ to some extent (to the value ofabout 25% on the abscissa). Formation of the C dots thus does notsignificantly lower the granularity. The use of the DY ink delays thetiming of starting formation of the C dots and thereby improves thegranularity.

In this simulative computation, since the DY ink contains the componentsof the Y ink, the LC ink and the LM ink (see the condition 6 givenabove), the formation of the DY dots decreases the dot recording ratioof the M dots. This gives a certain margin for the restriction of inkduty and delays the timing of starting formation of the K dots, thuspreventing the granularity from being worsened. As clearly understoodfrom the comparison between the results of the simulative computationwith the DY ink shown in FIG. 28A and the results of the simulativecomputation without the DY ink shown in FIG. 28B, the use of the DY inksignificantly delays the timing of starting formation of the K dots fromthe value of about 25% on the abscissa to the value of about 75%. Thismeans that the use of the DY ink remarkably prevents the granularityfrom being worsened.

FIG. 28C shows the results of the simulative computation without the DYink in the case of changing the restriction of ink duty set for theprinting paper from 220% to 260%. As clearly understood from thecomparison between FIG. 28B and FIG. 28C, the increase in restriction ofink duty delays the timing of starting formation of the K dots. Thecomparison between FIG. 28A and FIG. 28C, however, shows that theeffects attained by increasing the restriction of ink duty are less thanthe effects attained by the use of the DY ink. Even in the case of theprinting paper having the restriction of ink duty equal to 260%, the Cdots should start formation at the value of 0% on the abscissa. The useof the dark ink, on the other hand, delays the timing of startingformation of the C dots to the value of about 25% on the abscissa. Asdescribed previously, cyan is complementary to red. The C dots are thusrather conspicuous in the red background, although the degree ofconspicuousness is not so high as that of the K dots. The delayed timingof starting formation of the C dots to the value of about 25% on theabscissa by the use of the DY ink thus significantly improves thegranularity in the bright area (that is, the highlighted area).

As described above, in the process of printing a gradation pattern fromred to black, the change to the printing paper having the higherrestriction of ink duty improves the picture quality only in the shadowarea (that is, the area having large values on the abscissa). The use ofthe DY ink, on the other hand, improves the picture quality over thewhole range from the highlighted area to the shadow area.

C-5. Application to Printer with Three Color Inks

FIGS. 29A and 29B show the results of simulative computation in the caseof printing a gradation pattern from white to black with the colorprinter using only the C, M, and Y inks and not using the K ink. Unlikethe ‘black’ color expressed by the K ink, the ‘black’ color expressed bya combination of the C, M, and Y inks does not have a sufficiently lowlightness and gives an impression of dimness. In the case of printingthe ‘black’ color with the C, M, and Y inks, all the C dots, the M dots,and the Y dots should have dot recording ratios of 100%. FIG. 29A showsthe results of the simulative computation of the dot recording ratiowith regard to each color ink in this state. The sum of the dotrecording ratios of the respective color inks naturally exceeds therestriction of ink duty, and such settings of the dot recording ratiosare not practical. In other words, only the dim black color can beexpressed by the color printer using the three color inks, as long asthe practical dot recording ratios are set by taking into account therestriction of ink duty.

FIG. 29B shows the results of the simulative computation of the dotrecording ratio with regard to each ink in the case of using the DY dotsin addition to the C, M, and Y dots. In this simulative computation,since the DY ink contains the components of the LC ink, the LM ink, andthe Y ink (see the condition 6 given previously), replacement of the Ydots with the DY dots desirably decreases the dot recording ratios ofthe C dots and the M dots. The use of the DY dots accordingly enablesthe expression of the color of sufficiently clear black even when thepractical dot recording ratios are set by taking into account therestriction of ink duty.

As described above, the use of the DY ink enables the expression of thecolor of sufficiently clear black even without the K ink. The use of theDY ink instead of the K ink ensures the expression of the color ofsufficiently clear black and enables the image of high picture qualityto be printed with the color printer using the four color inks C, M, Y,and K and in the color printer using the six color inks including the LCand LM inks in addition to the above four color inks. In the prior artcolor printer using the four color inks or the six color inks,attachment of the ink cartridge for the DY ink in place of the inkcartridge for the K ink with the required operations, for example,rewriting the printer driver to a special printer driver for the DY ink,enables formation of the DY dots and prints an image of high picturequality including the sufficiently clear black color.

As described above with the results of the simulative computation, theuse of the DY ink enhances the degree of freedom in dot formation andthus improves the picture quality under a variety of printingconditions. The enhanced degree of freedom with the use of the DY inkenables images of low lightness but high saturation to be printedadequately. In many cases, the desired color can not be expressed insuch images because of the restriction of ink duty. The use of the DYink relieves the restriction of ink duty and thereby enables the colorexpressed on the printing paper to be closer to the desired color.

In the simulative computation discussed above, the DY ink satisfying theabove condition 6 was used as the DY ink. This DY ink is similar to theDY1 ink shown in FIG. 14D. The use of another DY ink similar to the DY2ink also exerts the similar effects as discussed below.

Based on the theory of subtractive mixture of colors, it is assumed thatthe K ink is equivalent to the combination of identical quantities ofthe C ink, the M ink, and the Y ink. According to the above conditions 4through 6, it is thought that the DY ink is obtained by adding ¼quantities of the C ink and the M ink to the Y ink. Since the K ink isequivalent to the combination of identical quantities of the C ink, theM ink, and the Y ink, the DY ink is thought to be the mixture of ¾quantity of the Y ink and ¼ quantity of the K ink. The ink thus obtainedis similar to the DY2 ink shown in FIG. 14E. The effects described abovewith the DY ink under the above conditions are thus also exerted by theDY2 ink.

In the actual printing operation, the condition that the K ink isequivalent to the combination of identical quantities of the C ink, theM ink, and the Y ink is not strictly fulfilled. The DY2 ink is, however,expected to have the qualitatively similar effects to those of the DY1ink. The DY3 ink having the significantly different spectroscopiccharacteristics in the area of the low sensitivity of vision to thecolor may also be used as the DY ink.

The simulative computation discussed above is carried out under thecondition 6 that the DY ink is equivalent to the ink including theidentical quantities of the LC ink and the LM ink in addition to the Yink. The rates of the LC ink and the LM ink added to the Y ink are,however, not restricted to this condition. As shown in FIG. 12, thecontents of the cyan dye and the magenta dye included in the DY ink areapproximately one quarter the contents of the cyan dye and the magentadye included in the C ink and the M ink, respectively. The contents ofthe dyes included in the DY ink are, however, not restricted to thiscomposition. Possible modification may vary the contents of the cyan dyeand the magenta dye or change the ratio of the cyan dye to the magentadye.

The decrease in rates of the dyes included in the DY ink increases thelightness of the DY ink. In this case, starting formation of the DY dotseven in the state of a relatively high lightness (that is, the state ofa small value on the abscissa in the graphs of FIGS. 25 through 29) doesnot make the DY dots conspicuous, thus not worsening the granularity.The increase in rates of the dyes included in the DY ink, on the otherhand, enables reduction of the greater numbers of the other color dotsby the formation of the DY dots. This accordingly enhances the effectsof improving the granularity based on the margin for the restriction ofink duty and saving the total quantity of ink consumption.

The present invention is not restricted to the above embodiment or itsmodifications, but there may be many other modifications, changes, andalterations without departing from the scope or spirit of the maincharacteristics of the present invention. For example, the software orapplication programs that actualize the above functions may be suppliedthrough a communication line to the main memory of the computer systemor an external storage device.

The scope and spirit of the present invention are limited only by theterms of the appended claims.

What is claimed is:
 1. A printing system comprising a printer thatcreates dots with a plurality of different inks, so as to print an imageon a printing medium, and a print controller that supplies controlinformation to said printer, so as to control the creation of dots withthe plurality of different inks, wherein said print controllercomprises: a dot on-off condition specification unit that specifies doton-off conditions with regard to a plurality of basic color inks and adark ink based on input image data, the plurality of basic color inksbeing combined with one another to express achromatic color, the darkink having a main wavelength region of light absorption substantiallyidentical with that of one basic color ink selected out of the pluralityof basic color inks but a lower lightness than that of the selectedbasic color ink; and a control information output unit that outputs thecontrol information to specify the dot on-off conditions with regard tothe plurality of basic color inks and the dark ink to said printer, saidprinter comprising: a control information input unit that receives thecontrol information to specify the dot on-off conditions with regard tothe plurality of basic color inks and the dark ink, which is output fromsaid control information output unit; and a dot formation unit thatcreates dots with the plurality of basic color inks and the dark ink,based on the input control information.
 2. A print controller thatsupplies control information to a printer, which creates dots with aplurality of different inks, in order to control the creation of dotswith the plurality of different inks, said printer creating dots with aplurality of basic color inks as well as with a dark ink, the pluralityof basic color inks being combined with one another to expressachromatic color, the dark ink having a main wavelength region of lightabsorption substantially identical with that of one basic color inkselected out of the plurality of basic color inks but a lower lightnessthan that of the selected basic color ink, said print controllercomprising: a dot on-off condition specification unit that specifies doton-off conditions with regard to the plurality of basic color inks andthe dark ink, based on input image data; and a control informationoutput unit that outputs the control information to specify the doton-off conditions with regard to the plurality of basic color inks andthe dark ink to said printer.
 3. A print controller in accordance withclaim 2, wherein said dot on-off condition specification unit comprises:a memory which stores a color conversion table, in which each tint usedto express a color image is mapped to a combination of the plurality ofbasic color inks and the dark ink to represent the tint, said dot on-offcondition specification unit specifying the dot on-off conditions withregard to the plurality of basic color inks and the dark ink byreferring to said color conversion table.
 4. A print controller inaccordance with claim 2, wherein said dot on-off condition specificationunit specifies the dot on-off conditions with regard to the plurality ofbasic color inks and the dark ink, based on a preset proportionregarding dots of the plurality of basic color inks and dots of the darkink.
 5. A print controller in accordance with claim 2, wherein the darkink has lower lightness and saturation than those of one basic color inkselected out of the plurality of basic color inks.
 6. A print controllerin accordance with claim 2, wherein the dark ink has a main wavelengthregion for most strongly absorbing a ray in a visible range, which issubstantially identical with that of one basic color ink selected out ofthe plurality of basic color inks, and a greater integral of lightabsorptivity in a wavelength region of the visible range than that ofthe selected basic color ink.
 7. A print controller in accordance withclaim 6, wherein the dark ink has the main wavelength region, which ismostly included in a wavelength region of 400 nm to 500 nm, and asmaller light absorptivity in the vicinity of 700 nm than a mean lightabsorptivity in a wavelength region of 600 nm to 700 nm.
 8. A printcontroller in accordance with claim 6, wherein the dark ink has the mainwavelength region, which is mostly included in a wavelength region of400 nm to 500 nm, and a greater light absorptivity in the vicinity of700 nm than a mean light absorptivity in a wavelength region of 600 nmto 700 nm.
 9. A print controller in accordance with claim 2, wherein thedark ink has: (A) a characteristic wavelength region for stronglyabsorbing a ray in a visible range to mainly determine the hue of thedark ink, which is substantially identical with a characteristicwavelength region of one basic color ink selected out of the pluralityof basic color inks; (B) a mean value of light absorptivity that isgreater than or substantially identical with a mean value of lightabsorptivity of the selected basic color ink in the characteristicwavelength region of the dark ink; and (C) a mean value of lightabsorptivity that is greater than a mean value of light absorptivity ofthe selected basic color ink in a wavelength region of visible lightexcept the characteristic wavelength region of the dark ink.
 10. A printcontroller in accordance with claim 9, wherein the dark ink has thecharacteristic wavelength region, which is mostly included in awavelength region of 400 nm to 500 nm, and a smaller light absorptivityin the vicinity of 700 nm than a mean light absorptivity in a wavelengthregion of 600 nm to 700 nm.
 11. A print controller in accordance withclaim 9, wherein the dark ink has the characteristic wavelength region,which is mostly included in a wavelength region of 400 nm to 500 nm, anda greater light absorptivity in the vicinity of 700 nm than a mean lightabsorptivity in a wavelength region of 600 nm to 700 nm.
 12. A printcontroller in accordance with claim 2, wherein the dark ink has a hue ina specific hue range interposed between a red hue zone and a green huezone on a Munsell hue circle, and a lower lightness than that of a basiccolor ink out of the plurality of basic color inks, which has a hue inthe specific hue range.
 13. A print controller in accordance with claim12, wherein the dark ink has a hue in the specific hue range thatincludes a yellow hue zone and extends to a boundary between the yellowhue zone and the green hue zone on the Munsell hue circle.
 14. A printcontroller in accordance with claim 12, wherein the dark ink has a huein the specific hue range that includes a yellow hue zone and extends toa boundary between the yellow hue zone and the red hue zone on theMunsell hue circle, and a smaller saturation than that of flesh color.15. A print controller in accordance with claim 2, wherein the dark inkhas a hue included in a specific range of 10R to 10GY on a Munsell huecircle, and a lower lightness than that of a basic color ink out of theplurality of basic color inks, which has a hue in the specific range.16. A print controller in accordance with claim 15, wherein the dark inkhas a saturation of smaller than 3.5C on a Munsell chroma when the hueof the dark ink is in a range of 2.5YR to 7.5YR on the Munsell huecircle.
 17. A print controller in accordance with claim 15, wherein thehue of the dark ink is in a range of 10YR to 10GY on the Munsell huecircle.
 18. A print controller in accordance with claim 15, wherein thedark ink has the hue in a range of 10Y to 10R on the Munsell hue circleand a saturation of smaller than 3.5C on a Munsell chroma.
 19. A printcontroller in accordance with claim 2, wherein said printer creates dotswith the plurality of basic color inks and the dark ink, as well as dotswith at least one light ink, the at least one light ink having a huesubstantially identical with that of at least one basic color inkselected out of the plurality of basic color inks but a lower densitythan that of the at least one basic color ink, said dot on-off conditionspecification unit specifies the dot on-off conditions with regard tothe plurality of basic color inks and the dark ink, as well as doton-off conditions with regard to the at least one light ink, and saidcontrol information output unit outputs the specification of the doton-off conditions with regard to the plurality of basic color inks, thedark ink, and the at least one light ink.
 20. A print controller inaccordance with claim 19, wherein the plurality of basic color inksinclude at least cyan ink, magenta ink, and yellow ink, the dark inkhaving a hue that is closest to the hue of the yellow ink among the cyanink, the magenta ink, and the yellow ink, specification of the doton-off conditions with regard to the dark ink being carried out toenable dots with the dark ink to be created after creation of dots withthe light ink when an image to be printed has hues varying from yellowto black.
 21. A print controller in accordance with claim 20, whereinthe light ink is light cyan ink having a hue substantially identicalwith that of the cyan ink but a lower density than that of the cyan ink.22. A print controller in accordance with claim 20, wherein the lightink is light magenta ink having a hue substantially identical with thatof the magenta ink but a lower density than that of the magenta ink. 23.A print controller in accordance with claim 20, wherein the dark inkhaving a hue that is closest to the hue of the yellow ink among the cyanink, the magenta ink, and the yellow ink, specification of the doton-off conditions with regard to the dark ink being carried out toenable dots with the dark ink to be created after creation of both dotswith light cyan ink, which has a hue substantially identical with thatof the cyan ink but a lower density than that of the cyan ink, and dotswith light magenta ink, which has a hue substantially identical withthat of the magenta ink but a lower density than that of the magentaink, when an image to be printed has hues varying from yellow to black.24. A print controller in accordance with claim 2, wherein said printercreates at least two variable-size dots having different sizes with theplurality of different inks, said dot on-off condition specificationunit specifies the dot on-off conditions with regard to the plurality ofdifferent inks and sizes of respective dots to be created by saidprinter, and said control information output unit outputs thespecification of the dot on-off conditions and the sizes of dots withregard to the plurality of different inks.
 25. A print controller inaccordance with claim 2, wherein said printer creates dots with theplurality of basic color inks including at least yellow ink, as well asdots with dark yellow ink that has a main wavelength region of lightabsorption substantially identical with that of the yellow ink but alower lightness than that of the yellow ink, said dot on-off conditionspecification unit specifies dot on-off conditions with regard to theplurality of basic color inks and the dark yellow ink, and said controlinformation output unit outputs the specification of the dot on-offconditions with regard to the plurality of basic color inks and the darkyellow ink.
 26. A print controller in accordance with claim 2, whereinthe plurality of basic color inks include at least cyan ink, magentaink, and yellow ink, the dark ink having a hue that is closest to thehue of the yellow ink among the cyan ink, the magenta ink, and theyellow ink, specification of the dot on-off conditions with regard tothe dark ink being carried out to enable dots with the dark ink to becreated together with dots of at least one of the basic color inks whenan image to be printed has hues varying from red to green on a Munsellhue circle.
 27. A print controller in accordance with claim 2, whereinthe plurality of basic color inks include at least cyan ink, magentaink, and yellow ink, the dark ink having a hue that is closest to thehue of the yellow ink among the cyan ink, the magenta ink, and theyellow ink, specification of the dot on-off conditions with regard tothe dark ink being carried out to enable dots with the dark ink to becreated prior to creation of dots with either one of the cyan ink andthe magenta ink when an image to be printed has hues varying from yellowto black.
 28. A print controller in accordance with claim 2, wherein theplurality of basic color inks include at least cyan ink, magenta ink,and yellow ink, the dark ink having a hue that is closest to the hue ofthe yellow ink among the cyan ink, the magenta ink, and the yellow ink,and a lower lightness than that of the yellow ink, specification of thedot on-off conditions with regard to the dark ink being carried out toenable dots with the dark ink to be created prior to creation of dotswith either one of the cyan ink and the magenta ink when an image to beprinted has hues varying from color of the either one of the cyan inkand the magenta ink to black.
 29. A print controller in accordance withclaim 2, wherein the plurality of basic color inks include at least cyanink, magenta ink, and yellow ink, the dark ink having a hue that isclosest to the hue of the yellow ink among the cyan ink, the magentaink, and the yellow ink, and a lower lightness than that of the yellowink, specification of the dot on-off conditions with regard to the darkink being carried out to enable dots with the dark ink to be createdafter creation of dots with the yellow ink when an image to be printedhas hues varying from color of either one of the cyan ink and themagenta ink to black.
 30. A print controller that supplies controlinformation to a printer, which creates dots with a plurality ofdifferent inks, in order to control the creation of dots with theplurality of different inks, said printer creating dots with a pluralityof basic color inks, which include at least cyan ink, magenta ink, andyellow ink, as well as with dark yellow ink, the dark yellow ink havinga main wavelength region of light absorption substantially identicalwith that of the yellow ink but a lower lightness than that of theyellow ink, said print controller comprising: a dot on-off conditionspecification unit that specifies dot on-off conditions with regard tothe plurality of basic color inks and the dark yellow ink, based oninput image data; and a control information output unit that outputs thespecification of the dot on-off conditions with regard to the pluralityof basic color inks and the dark yellow ink to said printer as thecontrol information.
 31. A printing apparatus that has a print head tocreate dots with a plurality of different inks on a printing medium,receives control information to control the creation of dots with theplurality of different inks, and actually creates dots with theplurality of different inks, based on the input control information, soas to print an image, said printing apparatus comprising: a basic colorink supply unit that supplies a plurality of basic color inks to saidprint head, the plurality of basic color inks being combined with oneanother to express achromatic color; a dark ink supply unit thatsupplies a dark ink to said print head, the dark ink having a mainwavelength region of light absorption substantially identical with thatof one basic color ink selected out of the plurality of basic color inksbut a lower lightness than that of the selected basic color ink; acontrol information input unit that receives the control informationwith regard to dots of the plurality of basic color inks and the darkink; and a dot formation unit that drives said print head based on theinput control information, so as to create dots with the plurality ofbasic color inks and the dark ink.
 32. A printing apparatus inaccordance with claim 31, wherein the plurality of basic color inksinclude at least cyan ink, magenta ink, and yellow ink.
 33. A printingapparatus in accordance with claim 31, wherein the plurality of basiccolor inks include at least cyan ink, magenta ink, yellow ink, and blackink and the dark ink is dark yellow ink having a main wavelength regionof light absorption substantially identical with that of the yellow inkbut a lower lightness than that of the yellow ink.
 34. A printingapparatus in accordance with claim 31, said printing apparatuscomprising: a light ink supply unit that supplies at least one light inkto said print head, the at least one light ink having a huesubstantially identical with that of at least one basic color inkselected out of the plurality of basic color inks but a lower densitythan that of the at least one basic color ink, wherein said controlinformation input unit receives the control information with regard todots of the at least one light ink, as well as with regard to the dotsof the plurality of basic color inks and the dark ink, and said dotformation unit creates dots with the at least one light ink as well asthe plurality of basic color inks and the dark ink, based on the inputcontrol information.
 35. A printing apparatus in accordance with claim31, wherein said print head enables at least two variable-size dotshaving different sizes to be created, said control information inputunit receives pieces of information regarding dot on-off conditions andsizes of dots to be formed by said print head with regard to theplurality of different inks as the control information, and said dotformation unit creates the at least two variable-size dots with theplurality of different inks, based on the input control information. 36.A printing apparatus in accordance with claim 31, said printingapparatus having an ink reservoir unit, in which the plurality of basiccolor inks and the dark ink are kept independently.
 37. A printingapparatus in accordance with claim 36, wherein said ink reservoir unitkeeps a greater quantity of the dark ink than a quantity of the onebasic color ink corresponding to the dark ink.
 38. A printing apparatusthat has a print head to create dots with a plurality of different inkson a printing medium, receives control information to control thecreation of dots with the plurality of different inks, and actuallycreates dots with the plurality of different inks, based on the inputcontrol information, so as to print an image, said printing apparatuscomprising: a basic color ink supply unit that supplies a plurality ofbasic color inks to said print head, the plurality of basic color inksincluding at least cyan ink, magenta ink, and yellow ink; a dark yellowink supply unit that supplies dark yellow ink to said print head, thedark yellow ink having a main wavelength region of light absorptionsubstantially identical with that of the yellow ink inks but a lowerlightness than that of the yellow ink; a control information input unitthat receives the control information with regard to dots of theplurality of basic color inks and the dark yellow ink; and a dotformation unit that drives said print head based on the input controlinformation, so as to create dots with the plurality of basic color inksand the dark yellow ink.
 39. A printing apparatus in accordance withclaim 38, said printing apparatus having an ink reservoir unit, in whichat least the cyan ink, the magenta ink, the yellow ink, and the darkyellow ink are kept independently, said ink reservoir unit keeping agreater quantity of the dark yellow ink than a quantity of the yellowink.
 40. A method of creating dots with a plurality of different inks,so as to print an image on a printing medium, said method comprising thesteps of: specifying dot on-off conditions with regard to a plurality ofbasic color inks and a dark ink based on input image data, the pluralityof basic color inks being combined with one another to expressachromatic color, the dark ink having a main wavelength region of lightabsorption substantially identical with that of one basic color inkselected out of the plurality of basic color inks but a lower lightnessthan that of the selected basic color ink; and creating dots with theplurality of basic color inks and the dark ink, based on thespecification of the dot on-off conditions with regard to the pluralityof basic color inks and the dark ink, so as to print an image.
 41. Amethod of supplying control information to a printer, which creates dotswith a plurality of different inks on a printing medium, in order tocontrol the creation of dots with the plurality of different inks andthereby controlling a printing operation of said printer, said methodcomprising the steps of: (a) specifying dot on-off conditions withregard to a plurality of basic color inks and a dark ink based on inputimage data, the plurality of basic color inks being combined with oneanother to express achromatic color, the dark ink having a mainwavelength region of light absorption substantially identical with thatof one basic color ink selected out of the plurality of basic color inksbut a lower lightness than that of the selected basic color ink; and (b)outputting the specification of the dot on-off conditions with regard tothe plurality of basic color inks and the dark ink to said printer asthe control information, so as to control the printing operation of saidprinter.
 42. A method in accordance with claim 41, said method furthercomprising the step of: (c) storing in advance mappings of tints used toexpress a color image to combinations of the plurality of basic colorinks and the dark ink to represent the tints, wherein said step (b)specifies the dot on-off conditions with regard to the plurality ofbasic color inks and the dark ink, based on the mappings stored inadvance.
 43. A method of supplying control information to a printer,which creates dots with a plurality of different inks on a printingmedium, in order to control the creation of dots with the plurality ofdifferent inks and thereby controlling a printing operation of saidprinter, said method comprising the steps of: (a) specifying dot on-offconditions with regard to a plurality of basic color inks and darkyellow ink based on input image data, the plurality of basic color inksincluding at least cyan ink, magenta ink, and yellow ink, the darkyellow ink having a main wavelength region of light absorptionsubstantially identical with that of the yellow ink but a lowerlightness than that of the yellow ink; and (b) outputting thespecification of the dot on-off conditions with regard to the pluralityof basic color inks and the dark yellow ink to said printer as thecontrol information, so as to control the printing operation of saidprinter.
 44. A method of receiving control information to controlcreation of dots with a plurality of different inks and driving a printhead, which creates dots with the plurality of different inks on aprinting medium, based on the control information, so as to print animage, said method comprising the steps of: (a) supplying a plurality ofbasic color inks and a dark ink to said print head, the plurality ofbasic color inks being combined with one another to express achromaticcolor, the dark ink having a main wavelength region of light absorptionsubstantially identical with that of one basic color ink selected out ofthe plurality of basic color inks but a lower lightness than that of theselected basic color ink; (b) receiving the control information withregard to dots of the plurality of basic color inks and the dark ink;and (c) driving said print head based on the input control informationto create dots with the plurality of basic color inks and the dark ink,thereby printing an image.
 45. A method of receiving control informationto control creation of dots with a plurality of different inks anddriving a print head, which creates dots with the plurality of differentinks on a printing medium, based on the control information, so as toprint an image, said method comprising the steps of: (a) supplying aplurality of basic color inks and dark yellow ink to said print head,the plurality of basic color inks including at least cyan ink, magentaink, and yellow ink, the dark yellow ink having a main wavelength regionof light absorption substantially identical with that of the yellow inkbut a lower lightness than that of the yellow ink; (b) receiving thecontrol information with regard to dots of the plurality of basic colorinks and the dark yellow ink; and (c) driving said print head based onthe input control information to create dots with the plurality of basiccolor inks and the dark yellow ink, thereby printing an image.
 46. Anink cartridge detachably attached to a printing apparatus, which printsan image with at least one ink, said ink cartridge keeping therein atleast one ink to be supplied to said printing apparatus, said inkcartridge comprising: a dark yellow ink reservoir that keeps thereindark yellow ink, the dark yellow ink having: (A) a characteristicwavelength region that is mostly in a wavelength range of 400 nm to 500nm, the characteristic wavelength region strongly absorbing a ray in avisible range to mainly determine the hue of the dark yellow ink; and(B) a mean value of absorptivity of the ray in the visible range exceptthe characteristic wavelength region, which ranges from 10% to 60%. 47.An ink cartridge in accordance with claim 46, said ink cartridge furthercomprising: a storage device that stores information regarding aquantity of ink in each of the ink reservoirs in a readable, writeableand volatile manner.
 48. An ink cartridge in accordance with claim 47,wherein said storage device has an ink quantity information storagearea, which is accessed to be written first by said printing apparatusand in which the information regarding the quantity of ink in each ofthe ink reservoirs is stored.
 49. An ink supplier that feeds a supply ofink to an ink cartridge, said ink cartridge being detachably attached toa printing apparatus and keeping therein at least one ink used by saidprinting apparatus, said ink supplier comprising: a sealed ink reservoirthat keeps an ink in a sealing manner; and an ink supply unit that feedsa supply of the sealed ink to said ink cartridge, wherein the ink sealedin said sealed ink reservoir has: (A) a characteristic wavelength regionthat is mostly included in a wavelength range of 400 nm to 500 nm, thecharacteristic wavelength region strongly absorbing a ray in a visiblerange to mainly determine the hue of the ink; and (B) a mean value ofabsorptivity of the ray in the visible range except the characteristicwavelength region, which ranges from 10% to 60%.
 50. A recording medium,in which a specific program is recorded in a computer readable manner,said specific program actualizing a method of creating dots with aplurality of different inks, so as to print an image on a printingmedium, said specific program causing a computer to attain the functionsof: specifying dot on-off conditions with regard to a plurality of basiccolor inks and a dark ink based on input image data, the plurality ofbasic color inks being combined with one another to express achromaticcolor, the dark ink having a main wavelength region of light absorptionsubstantially identical with that of one basic color ink selected out ofthe plurality of basic color inks but a lower lightness than that of theselected basic color ink; and controlling creation of dots with theplurality of basic color inks and the dark ink, based on thespecification of the dot-on-off conditions with regard to the pluralityof basic color inks and the dark ink.
 51. A recording medium, in which aspecific program is recorded in a computer readable manner, saidspecific program actualizing a method of supplying control informationto a printer, which creates dots with a plurality of different inks on aprinting medium, in order to control the creation of dots with theplurality of different inks and thereby controlling a printing operationof said printer, said specific program causing a computer to attain thefunctions of: specifying dot on-off conditions with regard to aplurality of basic color inks and a dark ink based on input image data,the plurality of basic color inks being combined with one another toexpress achromatic color, the dark ink having a main wavelength regionof light absorption substantially identical with that of one basic colorink selected out of the plurality of basic color inks but a lowerlightness than that of the selected basic color ink; and outputting thespecification of the dot on-off conditions with regard to the pluralityof basic color inks and the dark ink to said printer as the controlinformation, so as to control the printing operation of said printer.52. A recording medium in accordance with claim 51, wherein saidspecific program further causes the computer to attain the function of:storing in advance mappings of tints used to express a color image tocombinations of the plurality of basic color inks and the dark ink torepresent the tints, and the dot on-off conditions with regard to theplurality of basic color inks and the dark ink are specified, based onthe mappings stored in advance.
 53. A recording medium, in which aspecific program is recorded in a computer readable manner, saidspecific program actualizing a method of supplying control informationto a printer, which creates dots with a plurality of different inks on aprinting medium, in order to control the creation of dots with theplurality of different inks and thereby controlling a printing operationof said printer, said specific program causing a computer to attain thefunctions of: specifying dot on-off conditions with regard to aplurality of basic color inks and dark yellow ink based on input imagedata, the plurality of basic color inks including at least cyan ink,magenta ink, and yellow ink, the dark yellow ink having a mainwavelength region of light absorption substantially identical with thatof the yellow ink but a lower lightness than that of the yellow ink; andoutputting the specification of the dot on-off conditions with regard tothe plurality of basic color inks and the dark yellow ink to saidprinter as the control information, so as to control the printingoperation of said printer.
 54. A recording medium, in which a specificprogram is recorded in a computer readable manner, said specific programactualizing a method of receiving control information to controlcreation of dots with a plurality of different inks and driving a printhead, which creates dots with the plurality of different inks on aprinting medium, based on the control information, so as to print animage, said specific program causing a computer to attain the functionsof: receiving the control information to control creation of dots with aplurality of basic color inks and a dark ink, the plurality of basiccolor inks being combined with one another to express achromatic color,the dark ink having a main wavelength region of light absorptionsubstantially identical with that of one basic color ink selected out ofthe plurality of basic color inks but a lower lightness than that of theselected basic color ink; and driving said print head based on the inputcontrol information to create dots with the plurality of basic colorinks and the dark ink, thereby printing an image.
 55. A recordingmedium, in which a specific program is recorded in a computer readablemanner, said specific program actualizing a method of receiving controlinformation to control creation of dots with a plurality of differentinks and driving a print head, which creates dots with the plurality ofdifferent inks on a printing medium, based on the control information,so as to print an image, said specific program causing a computer toattain the functions of: receiving the control information to controlcreation of dots with a plurality of basic color inks and dark yellowink, the plurality of basic color inks including at least cyan ink,magenta ink, and yellow ink, the dark yellow ink having a mainwavelength region of light absorption substantially identical with thatof the yellow ink but a lower lightness than that of the yellow ink; anddriving said print head based on the input control information to createdots with the plurality of basic color inks and the dark yellow ink,thereby printing an image.